What is the meaning of آ?

Alif maddah. A double-alif used to write the sequence /ʔaː/.

A form of the initial interrogative particle that indicates a yes-or-no question. As it is written together with the following word, when this word begins with ال (al-, “the”) they are orthographically morphed together and written with a مَدَّة (madda) diacritic instead of maintaining both.

I (nominative)

A letter of the Khowar alphabet, written in the Arabic script; preceded by ا and followed by أ, the first variant letter of alif.

It is used to represent the sound “a” in words written in Ottoman Turkish. In words of Turkish origin, it appears only at the beginning of a sentence.

A vowel of Pahari-Potwari, written in the Shahmukhi script.

The first letter of the Ushojo alphabet, written in the Arabic script; followed by أ.

and

A letter of the Kashmiri alphabet, written in the Arabic script; preceded by اَ (a) and followed by أ, a vowel.

yes, yeah

alif with madda, a form of ا, the first letter of the Pashto alphabet

Alif maddah

present stem form of آمدن (âmadan)

A vowel of Punjabi, written in the Shahmukhi script. The variant of alif used for initial /aː/.

inflection of آݨا (āṇā):

1. stem
2. second-person singular familiar imperative

stem

second-person singular familiar imperative

A vowel of Urdu, the variant of alif used for initial /aː/.

Source: wiktionary.org