What is the meaning of Modifier?

One who, or that which, modifies.

A word, phrase, or clause that limits or qualifies the sense of another word or phrase. (It may be any of the following: an adjective phrase, an adverb phrase, a prepositional phrase, a noun phrase, or a subordinate clause.)

A keyword that qualifies the meaning of other code.

Short for modifier key.

to change, modify

Source: wiktionary.org