What is the meaning of أ?

The first letter of the Arabic alphabet is the small hamza (ء) that sits on top of أ, and the tall column is its bearer. The composite letter is called أَلِف (ʔalif) and the hamza represents a glottal stop (/ʔ/). (See also ا.) It is followed by ب (b).

introduces a positive yes-no question

introduces a negative yes-no question

indicates an exclusive disjunction with أَمْ (ʔam, or), as in alternative questions

indicates an inclusive disjunction with أَمْ (ʔam, or) that denotes sameness, indistinguishability, unimportance, insignificance, or indifference

a vowel of Kashmiri.

The second other alif letter of the Khowar abjad.

The first letter of the Kyrgyz alphabet.

The second letter of the Ushojo abjad.

The first letter of the Malay alphabet, written in the Arabic script.

The first letter of the Persian alphabet.

Source: wiktionary.org