Young people sometimes use mega in front of adjectives or adverbs in order to emphasize them. [informal, emphasis]

Young people sometimes use mega in front of nouns in order to emphasize that the thing they are talking about is very good, very large, or very impressive. [informal, emphasis]

Mega- is added to nouns that refer to units of measurement in order to form other nouns referring to units that are a million times bigger.

Mega- combines with nouns and adjectives in order to emphasize the size, quality, or importance of something. [informal, emphasis]