Terminology

There are a couple listings out on the web, let's do a nice merge.

Japanese	English	Explanation
ari	in effect	States that the preceding rule is used, as in akadora ari for playing with red fives. Opposite of nashi.
nashi	invalid	States that the preceding rule is not in effect, as in kuikae nashi for disallowing players to call a tile and immediately discard another tile which would have also completed the called meld.
shuntsu	sequence	Three tiles of the same suit in sequence, used as one of the four melds in a regular hand. Chii is used to call a tile to complete a shuntsu and set it aside as a minjun, i.e., an open shuntsu. A concealed shuntsu is an anjun.