A Lewis acid is a species that accepts a pair of electrons from another species; in other words, it is an electron pair acceptor.
ɐ lˈuːɪs ˈæsɪd ɪz ɐ spˈiːsiːz ðæt ɐksˈɛpts ɐ pˈɛɹ ʌv ᵻlˈɛktɹɑːnz fɹʌm ɐnˈʌðɚ spˈiːsiːz; ɪn ˈʌðɚ wˈɜːdz, ɪɾ ɪz ɐn ᵻlˈɛktɹɑːn pˈɛɹ ɐksˈɛptɚ.