A

A is the first letter of the English alphabet. It is a vowel used in a sentence before a noun. It is also used to refer to a unit of measurement, for example, 'a thousand'.

If there are sets of items, categories, sizes etc, it is generally used to denote the first in a set.

In academics, A is the highest class of mark.

In a game of chess, 'a' refers to the first file from the lest when viewed from white's side.

In algebra, 'a' is usually the first fixed quantity.

In human biology, A is a blood group.

In music, it is the sixth note of the diatonic scale of C major.