R Stringdb bioconductor
The terms_id is meant to be a vector of GO or KEGG IDs that annotate to the proteins of interest. As it's described, the method get_term_protein:


  Returns the proteins annotated to belong to a given term.


My substantiation in part comes from the vignettes for STRINGdb that use terms in a separate set of functions like so:

&gt;head(enrichmentGO, n=7)
term_id proteins hits pvalue pvalue_fdr
1 GO:0048545 383 15 2.337593e-07 0.000368020
2 GO:0006952 1286 28 3.806997e-07 0.000368020
3 GO:0002252 405 15 4.756829e-07 0.000368020
4 GO:0010466 234 11 1.767763e-06 0.001025745
5 GO:0045861 330 12 8.407161e-06 0.003765892
6 GO:0010951 228 10 9.735179e-06 0.003765892
7 GO:0002443 141 8 1.224368e-05 0.003839606
term_description
1 response to steroid hormone
2 defense response
3 immune effector process
4 negative regulation of peptidase activity
5 negative regulation of proteolysis
6 negative regulation of endopeptidase activity
7 leukocyte mediated immunity
&gt;head(enrichmentKEGG, n=7)
term_id proteins hits pvalue pvalue_fdr
1 04115 66 6 9.969204e-08 1.475442e-05
2 04610 68 5 3.577966e-06 2.647695e-04
3 05168 174 5 3.254067e-04 1.605340e-02
4 01100 1161 12 5.277721e-04 1.952757e-02
5 04380 123 4 8.399948e-04 2.486385e-02
6 00590 61 3 1.197959e-03 2.638087e-02
7 05161 139 4 1.322517e-03 2.638087e-02
term_description
1 p53 signaling pathway
2 Complement and coagulation cascades
3 Herpes simplex infection
4 Metabolic pathways
5 Osteoclast differentiation
6 Arachidonic acid metabolism
7 Hepatitis B


And so usage would follow, for example, I want proteins that associate with cell growth, I can use c("GO:0016049") as my terms_id to retrieve that list. 

library(STRINGdb) #load package

string_db &lt;- STRINGdb$new(version="10", species=9606, score_threshold=0, input_directory="") #set environment, 9606=human

string_db$get_term_proteins(c("GO:0016049")) #use new environment variable to query the database, 0016049 refers to cell cycle just as an example.


Output (annotation column w/ text descriptions removed for brevity):

               STRING_id    term_id preferred_name protein_size
1   9606.ENSP00000002829 GO:0016049         SEMA3F          785
2   9606.ENSP00000211998 GO:0016049            VCL         1134
3   9606.ENSP00000212355 GO:0016049         TGFBR3          851
4   9606.ENSP00000216037 GO:0016049           XBP1          261
5   9606.ENSP00000216911 GO:0016049          AURKA          403
6   9606.ENSP00000221930 GO:0016049          TGFB1          390
7   9606.ENSP00000225792 GO:0016049           DDX5          614
8   9606.ENSP00000230732 GO:0016049         POU4F3          338
9   9606.ENSP00000238682 GO:0016049          TGFB3          412
10  9606.ENSP00000239462 GO:0016049            TNN         1299
11  9606.ENSP00000245479 GO:0016049           SOX9          509
12  9606.ENSP00000255448 GO:0016049          DCLK1          729
13  9606.ENSP00000256951 GO:0016049           EMP1          157
14  9606.ENSP00000258106 GO:0016049           EMX1          290
15  9606.ENSP00000258743 GO:0016049            IL6          212
16  9606.ENSP00000261023 GO:0016049          ITGAV         1048
17  9606.ENSP00000261918 GO:0016049         SEMA7A          666
18  9606.ENSP00000262017 GO:0016049          ITGB3          788
19  9606.ENSP00000263713 GO:0016049        EPB41L5          733
20  9606.ENSP00000263980 GO:0016049         SLC9A1          815
21  9606.ENSP00000264057 GO:0016049           DGKD         1214
22  9606.ENSP00000264279 GO:0016049          NOP58          529
23  9606.ENSP00000265136 GO:0016049           COBL         1261
24  9606.ENSP00000265362 GO:0016049         SEMA3A          771
25  9606.ENSP00000265371 GO:0016049           NRP1          923
26  9606.ENSP00000266058 GO:0016049          SLIT1         1534
27  9606.ENSP00000268182 GO:0016049         IQGAP1         1657
28  9606.ENSP00000270221 GO:0016049           EMP3          163
29  9606.ENSP00000272134 GO:0016049         LEFTY1          366
30  9606.ENSP00000276416 GO:0016049           BIN3          253
31  9606.ENSP00000278671 GO:0016049        LAMTOR1          161
32  9606.ENSP00000281321 GO:0016049         POU4F2          409
33  9606.ENSP00000283027 GO:0016049          NUBP1          320
34  9606.ENSP00000284981 GO:0016049            APP          770
35  9606.ENSP00000296388 GO:0016049         LEPRE1          736
36  9606.ENSP00000296755 GO:0016049          MAP1B         2468
37  9606.ENSP00000296875 GO:0016049           GDF9          454
38  9606.ENSP00000301067 GO:0016049           MLL2         5537
39  9606.ENSP00000303351 GO:0016049          ITGB1          798
40  9606.ENSP00000305133 GO:0016049          SOCS5          536
41  9606.ENSP00000306157 GO:0016049           IL7R          459
42  9606.ENSP00000306662 GO:0016049         ADRA1B          520
43  9606.ENSP00000307156 GO:0016049          LAMB2         1798
44  9606.ENSP00000307272 GO:0016049          RPTOR         1335
45  9606.ENSP00000316357 GO:0016049          USP9X         2570
46  9606.ENSP00000316543 GO:0016049          RAPH1         1250
47  9606.ENSP00000317257 GO:0016049          CPNE1          542
48  9606.ENSP00000322957 GO:0016049           PAK7          719
49  9606.ENSP00000324549 GO:0016049         CYFIP1         1253
50  9606.ENSP00000324560 GO:0016049           ULK1         1050
51  9606.ENSP00000324856 GO:0016049          STK11          433
52  9606.ENSP00000329623 GO:0016049           BCL2          239
53  9606.ENSP00000330382 GO:0016049          PDGFB          241
54  9606.ENSP00000332643 GO:0016049            NDN          321
55  9606.ENSP00000333982 GO:0016049          NDEL1          345
56  9606.ENSP00000334458 GO:0016049          GATA4          442
57  9606.ENSP00000335246 GO:0016049         ENTPD5          428
58  9606.ENSP00000337146 GO:0016049          ENOX2          610
59  9606.ENSP00000337332 GO:0016049          SIRT6          355
60  9606.ENSP00000337697 GO:0016049            DCX          441
61  9606.ENSP00000339740 GO:0016049         CAMK2D          499
62  9606.ENSP00000340820 GO:0016049           MAPT          776
63  9606.ENSP00000341940 GO:0016049           CAV3          151
64  9606.ENSP00000347906 GO:0016049          PRMT2          433
65  9606.ENSP00000348769 GO:0016049          ARIH2          493
66  9606.ENSP00000351049 GO:0016049           PAK4          591
67  9606.ENSP00000351591 GO:0016049          NLGN3          848
68  9606.ENSP00000351905 GO:0016049         TGFBR2          592
69  9606.ENSP00000353362 GO:0016049        CACNA1A         2506
70  9606.ENSP00000353582 GO:0016049           NRP2          931
71  9606.ENSP00000354558 GO:0016049           MTOR         2549
72  9606.ENSP00000354829 GO:0016049          SGMS1          413
73  9606.ENSP00000354877 GO:0016049           ULK2         1036
74  9606.ENSP00000355627 GO:0016049            AGT          485
75  9606.ENSP00000355785 GO:0016049         LEFTY2          366
76  9606.ENSP00000355896 GO:0016049          TGFB2          442
77  9606.ENSP00000357288 GO:0016049        LAMTOR2          125
78  9606.ENSP00000357470 GO:0016049           IL6R          468
79  9606.ENSP00000357494 GO:0016049           ROS1         2347
80  9606.ENSP00000359095 GO:0016049          PRMT6          375
81  9606.ENSP00000359729 GO:0016049         SLC9A6          701
82  9606.ENSP00000360973 GO:0016049          AGTR2          363
83  9606.ENSP00000360988 GO:0016049          LUZP4          313
84  9606.ENSP00000361423 GO:0016049           ABL1         1149
85  9606.ENSP00000362092 GO:0016049          RRAGC          399
86  9606.ENSP00000362717 GO:0016049           LHX2          406
87  9606.ENSP00000363822 GO:0016049             AR          920
88  9606.ENSP00000365663 GO:0016049           NPPA          151
89  9606.ENSP00000366396 GO:0016049           XRN2          950
90  9606.ENSP00000367123 GO:0016049         SLC3A2          631
91  9606.ENSP00000367830 GO:0016049          PRKCZ          592
92  9606.ENSP00000368030 GO:0016049         ATAD3A          634
93  9606.ENSP00000368169 GO:0016049           DVL1          670
94  9606.ENSP00000368683 GO:0016049           EDN1          212
95  9606.ENSP00000369014 GO:0016049           NDNF          568
96  9606.ENSP00000369816 GO:0016049           SHBG          402
97  9606.ENSP00000369960 GO:0016049         ADRA1A          475
98  9606.ENSP00000370330 GO:0016049        ERBB2IP         1371
99  9606.ENSP00000376800 GO:0016049           MTPN          118
100 9606.ENSP00000377823 GO:0016049          NDRG4          391
101 9606.ENSP00000377947 GO:0016049           RARG          454
102 9606.ENSP00000378306 GO:0016049         PPP3CB          525
103 9606.ENSP00000379003 GO:0016049          NUPR1          100
104 9606.ENSP00000385610 GO:0016049          MEX3C          659
105 9606.ENSP00000395359 GO:0016049          CADM1          442
106 9606.ENSP00000411672 GO:0016049       ATP6V0E2          213
107 9606.ENSP00000414303 GO:0016049           BDNF          329
108 9606.ENSP00000419782 GO:0016049           CDK5          292
109 9606.ENSP00000422591 GO:0016049          SLIT2         1529
110 9606.ENSP00000427941 GO:0016049       ATP6V0E1           81
111 9606.ENSP00000430333 GO:0016049          SLIT3         1523
112 9606.ENSP00000465742 GO:0016049        RASGRP4          673