A modifier is a word or phrase, or clause that functions as an adjective or adverb. It provides additional information about another word or phrase. It is also known as an adjunct.
Modifier is of two types; Pre-modifier and Post-modifier
When modifiers appear before the head are called Pre- Modifier, and while modifiers appear after the head are called Post- Modifier.
Modifiers may be either restrictive (essential to the meaning of a sentence) or non-restrictive (additional but not essential elements in a sentence).