The term for Tetris’s preview of upcoming pieces is the queue.
In modern Tetris, the queue is the display showing pieces that will become available after the current tetromino. It lets players plan placements several moves ahead instead of reacting only to the piece currently falling. The exact number of visible pieces varies by game and interface, but the underlying idea is the same: a sequence of upcoming tetrominoes.
Queue is often confused with Hold. Hold is the separate storage slot that lets a player set aside the active piece and retrieve it later, usually with a one-piece swap restriction. The Matrix is the playfield itself, while Stack describes the pile of placed blocks rather than the preview sequence.
The queue is especially important in competitive and modern guideline-based Tetris, where players use it to prepare line clears, avoid creating holes, and build setups such as T-spins. Its predictability depends on the game’s randomizer. In many modern implementations, pieces are generated through a seven-piece bag, so knowing the visible queue provides useful information without revealing the entire future sequence.
Thus, “queue” names the preview mechanism, while Hold names the player-controlled reserve slot.