Modification describes the grammatical process in which the semantic value of a word (usually a noun, verb or adjective) can be 'modified' or changed by the addition of another word or phrase (usually an adjective or adverb).

For example, nouns can be both pre-modified (by adjectives, e.g. A tall dark stranger' or other nouns, e.g. 'oven glove') as well as post-modified, e.g. 'The man with an ice-cream. Prepositional phrases can also act as modifiers when they act as the complement of a verb, as in, 'The man is a pig!'.

» Linguistic Library (Mike Green)