A feature of most newer Tetris games that let you hold a piece you don't want. For example, if you want to use an L Piece instead of a Line Piece, you can hold it by it's assigned button.
A feature of most newer Tetris games that let you drop a piece instantly. This is used in multiplayer games to encourage speed and thinking competetively.
This shows you what is the next piece that you need to place in order to be able to clear lines
This is an obsactle used in multiplayer games to increase randomized lines of blocks appear at the bottom of the playing field.
The system for how pieces behave, SRS represents where and how pieces spawn and how they rotate. All pieces spawn horizontally and wholly above the playfield. The I and O pieces spawn centrally, and the other, 3-cell wide pieces spawn rounded to the left. The J, L and T spawn pointing up. In Tetris Worlds, the tetrominoes spawn in rows 22 and 23 (or just row 22 in the case of the "I" tetromino), however, in later games the tetrominoes spawn 1 row lower.