Deckbuilder
Also said as Deck-building game, Roguelike deckbuilder
You start with a small and weak deck of cards, and you improve it as you play, adding and removing cards between hands or fights. It promises the delight of watching a pile of cards become a machine.
Each new card makes the others better or worse, and every card added dilutes the draw. This makes a small choice interesting, and a bad deck is your own doing.
Say it
“Deckbuilder rules: three energy a turn, five cards drawn, and show what every enemy will do. After each fight offer one of three cards, or let the player skip so that a thin deck is a real plan.”
Where you’ve seen it
Dominion (2008), by Donald X. Vaccarino, invented the form on the tabletop. Slay the Spire (2019) put it into a roguelike run with three energy a turn, and showed each enemy's intent, so that every turn became a small, fair puzzle.
Not to be confused with collectible card game
In a collectible card game you build the deck before you play, often buying the cards. In a deckbuilder, building the deck is the game.