Garbage is a form of "attack" in multiplayer Tetris that has been around since the days of the Game Boy. The basic gist of it is that if you clear multiple rows of tetrominoes at one time, extra rows with gaps will be added to the bottom of your opponent's playfield.
The garbage system is simple. The more rows you clear at once, the more garbage rows are sent to your opponent.
General Garbage System in Guideline Games
|Clear Type||Rows Cleared||Garbage Rows Sent|
The left diagram shows the player's field while the right shows his opponent.
If a player drops a "T" here:
It will clear two lines at once, sending one row of garbage to the opponent:
Then, if the player drops a tetris here: