What is the meaning of א?

The first letter of the Hebrew alphabet.

(a transfinite cardinal number)

Aleph or alef: the first letter of the Hebrew alphabet, coming before ב.

The numeral 1 in Hebrew numbering.

and

The first letter in the Yiddish alphabet, שטומער־אַלף (precedes ו or י to indicate a word-initial vowel)

Source: wiktionary.org