Administrator
The Administrator is by default the creator of the server. But on LFJR for exemple,there's a few because they're in charge of the server.

client
A client is just a person playing that is not the server. A client connects to a server. Find the IP of a server with people you want to play with and put that in to the correct edit box. Then put your nickname in the Nickname box and press the Connect button. You should then see the nicknames playing pop up in the partyline window and any teams the players are on. When the game has started, click on the Show Fields button and a window with all 6 fields will be shown. The fields will be updated every time a player's block is placed onto their field to keep everyone updated on who's winning.

Combos
Combos are chain reactions wanted or not in some cases. I add that Combos are only for Quadra.

Double rotation
Double rotation is a control of both rotations to left and right.

Pure
Pure is a mode for tetrinet and tetrifast without bonus used on specs (A, B, C, G, N, Q, R, S, O). It used to have 15% stick but there's channels like #pure20 with 20% stick or #pure25 with 25% stick.

SNS
SNS is the contraction of "Stick N' Square". So in this mode, you only have this 2 kinds of blocks.

Specs
On the language of TetriNET, to play in specs means to play with bonus whatever they are (2:1 = 2 lines / bonus) ou (1:1 = 1 line / bonus).