Toitsu

Toitsu 「対子」 are generic tile pairs. They may occur at any time during the development of a hand. Regardless, every hand requires at least one pair for completion, even kokushi musou.

Fu

Main article: Scoring

Specific tile pairs generate fu. Pairs of yakuhai tiles count for 2 fu.

Chiitoitsu

Main article: Chiitoitsu

One yaku is specifically defined as a collection of pairs. Chiitoitsu is directly translated as "seven pairs".