Type-C Cable : Different between Active cable, Passive Cable, EMCA
"Active cable" has "additional electronics" called "re-driver". USB 3.x signal pairs are unidirectional. When a signal propagates along a cable, it gets unevenly attenuated and loses its original shape. A re-driver takes input signal, and amplifies and shapes it up (adds de-emphasis and equilization) to correct the signal degradation over physical channel (cable's transmission line). The other channel works in opposite direction. General description can be found in here, and details in this ElectronicsDesign article. 

Re-driver ICs are manufactured by several companies like TI, NXP, Pericom/Diodes, PI2EQX502 is an example.