In the hexadecimal (base 16) numbering system, A is a number that corresponds to the number 10 in decimal (base 10) counting.
ɪnðə hˈɛksɐdˌɛsɪməl bˈeɪs sˈɪkstiːn nˈʌmbɚɹɪŋ sˈɪstəm, ɐ ɪz ɐ nˈʌmbɚ ðæt kˌɔːɹɪspˈɑːndz tə ðə nˈʌmbɚ tˈɛn ɪn dˈɛsɪməl bˈeɪs tˈɛn kˈaʊntɪŋ.