What is the meaning of अ?

the first letter and first vowel of the Devanagari script

The first vowel of Dhivehi, written in Devanagari script.

the first vowel of Hindi, written in the Devanagari script; inherent after consonants

The first vowel in Marathi.

The first vowel of Nepali, written in the Devanagari script. Inherent after consonants.

The first vowel of Sanskrit, written in the Devanagari script. Inherent after consonants.

A vocative particle; o, oh

An interjection of pity; ah

a pronominal base

Source: wiktionary.org