As a letter:
* The first letter of the alphabet.
* Used to indicate a grade, usually representing excellent performance.
As an article:
* Used before singular countable nouns to indicate a specific, but unspecified, item. For example, "an apple," "a book."
* Used before singular countable nouns beginning with a consonant sound. For example, "a cat," "a house."
As an abbreviation:
* Can stand for "am" or "about" in informal writing.
In other contexts:
* "A" can be used as a symbol for a specific thing, such as a blood type.
* In music, "A" refers to a note in the musical scale.
Could you provide more context? If you tell me where you saw the word "a," I can help you understand what it means in that specific case.