What is the meaning of 9?

The cardinal number nine.

A digit in the decimal system of numbering, and also hexadecimal.

tone number 9, in some cases when the language does not have the usual 4 to 8 categories.

Clipping of 900 (900° spin).

alternative form of  /

alternative form of (gau, unpleasant person)

alternative form of  /

Source: wiktionary.org