Jantou
Jantou「雀頭」 is the pair of a winning hand; every hand requires (at least) one pair to win. In English, it is usually called a "pair", but occasionally called an "eye".
Fu
If the hand's pair is composed of yakuhai tiles, the pair is worth 2 fu:
A wind tile that is both the seat and round wind may be worth 2 fu or 4 fu, depending on the ruleset.
All other pairs are worth 0 fu.
Tanki
Only one basic wait involves the pair directly: tanki ("pair wait"). This pattern occurs when the hand contains four complete tile groups and waits to complete the pair.