ZZZZ
This term is used to express annoyance at the slow speed of another player at the table. There is no set number of z's to be used. Generally the more z's used, the more annoyed the player is. This is really only used when a player is repeatedly slow to act - not just when ever any player takes a few seconds.

Strangely enough, a player repeatedly writing zzz's in the chat box can also be very annoying, and can slow up a game further.