You're going on "Are You Smarter Than A Fifth Grader" aren't you.
Modifiers are adjectives and adverbs that modify the sense of a noun or verb.
For example:
"A red ball" red refers to the ball and modifies it as a thing, therefore red is the modifier.
additionally you could have something like "Bob danced quickly", quickly is the modifier.
I've actually never heard the term "modifier" used before, and I was an english major, but according to the definition that's what it refers to.
