What is the meaning of 3?

The cardinal number three.

A digit in the decimal system of numbering, as well as octal, and hexadecimal.

The cube of a number or a unit.

the pitch of a tone, perhaps most commonly mid-pitch, but it may instead be high or low depending on local convention (e.g. the highest or lowest pitch if only the numbers 13 are used)

tone number 3, typically identified with dark rising yin shang (陰上). May be identified with departing qu tone () if the yinyang distinction is not made.

Clipping of 360. (360° spin)

Alternative transliteration of .

Used after an isolated affix or clitic to indicate that it has three variant forms, dependent on the vowel harmony of the preceding stem or word.

Source: wiktionary.org