"A" is often used to denote something or someone of a better or more prestigious quality or status: A−, A or A+, the best grade that can be assigned by teachers for students' schoolwork; "A grade" for clean restaurants; A-list celebrities, etc.
"ˈeɪ" ɪz ˈɔfən jˈuːzd tə dᵻnˈoʊt sˈʌmθɪŋ ɔːɹ sˈʌmwʌn əvə bˈɛɾɚ ɔːɹ mˈoːɹ pɹɛstˈɪdʒəs kwˈɔlᵻɾi ɔːɹ stˈæɾəs: ɐ mˈaɪnəs, ɐ ɔːɹ ɐ plˈʌs, ðə bˈɛst ɡɹˈeɪd ðæt kæn biː ɐsˈaɪnd baɪ tˈiːtʃɚz fɔːɹ stˈuːdənts skˈuːlwɜːk; "ɐ ɡɹˈeɪd" fɔːɹ klˈiːn ɹˈɛstɹɑːnts; ˈeɪlˈɪst səlˈɛbɹᵻɾiz, ɛtsˈɛtɹə.