What does the phrase a mean?

The phrase "a" is not a phrase, but rather a definite article. It's used before singular nouns to indicate that the noun is referring to a specific, but unspecified, member of a group.

Here are some examples:

* "I saw a cat in the yard." This means you saw one cat, but it doesn't specify which cat.

* "Can you pass me a pencil?" This means you want any pencil, not a specific one.

"A" is also used before words that begin with a consonant sound, even if the first letter is a vowel. For example:

* "a university"

* "a European country"

To summarize, "a" is used to indicate a singular, unspecified item.