The term Events Team has come to refer to a group of officials on a server that organise special events to entertain players. These vary in theme dramatically, but usually involve some element of competition (trivia, sparring contests, etc) and reward (specific to the server - sometimes money, sometimes items, sometimes special tokens).
As with 'LAT' and 'NAT', the abbreviation 'ET' is often used to refer to individual members of the Events Team rather than the whole.