Broad, Exact, Phrase and Negative are all keyword match types they are explained in detail in the Match Types page.
Match types are defined around criteria that describe how a user's query relates to purchased keywords. A match type is defined by having one or more of the following properties:
Additional words in query?Whether the query can contain additional words and still match the advertisement.
Variant normalisation?Operations such as removing diacritics from characters ("café" to "cafe") or transforming to the base form ("fuß" to "fuss")
Lemmatisation?Reduces the word to its lemma or canonical form (e.g. "boxing" to "box").
Synonyms?Whether matches against synonyms are accepted.
Order sensitive?Whether words must be in the same order in both the query and purchased keyword.
Contiguous?Whether the words must be next to each other in one "run" or "phrase" or whether other words can be found in the middle of the phrase.