Broad, phrase, exact
Broad matches related searches and variations — widest reach, most discovery, most wasted clicks. Phrase matches searches containing your phrase in order — a middle ground. Exact matches only the exact term — tightest control, lowest waste, least reach.
A simple strategy
Use broad and phrase (and automatic campaigns) to discover converting search terms, then add the winners as exact for control. This "discover wide, harvest tight" loop is the core of efficient keyword management.
Negative match types matter too
Broad match will find wasteful searches. Block them with negative keywords — negative exact for a single phrase, negative phrase to block anything containing it. AIAdKing harvests winners and adds negatives automatically every night.