Worker Placement is a game mechanic used in many board games. In this type of game each player gets a certain number of tokens -- the 'workers' -- and has a number of tasks they can allot them to for each round of the game. Either the number of workers or access to choice placements will usually be highly limited, resulting in stiff competition. Most often access to the slots is determined through drafting, although some games involve bidding or purchasing choice slots. At the end of the round the workers are returned and the placement starts again. These games often require players to bootstrap the number of workers available to a player, or have requirements to 'feed' or 'pay' workers if players want to keep them for the next round.
This is one of the more common game mechanics, and is used by a number of popular games: Agricola, Caverna: The Cave Farmers, Caylus, The Pillars of the Earth, The Manhattan Project, Lords of Waterdeep, Scythe, Cuba, The Taverns Of Tiefenthal, and Dice City, among many others.
These games have a wide range of variation. In Scythe the primary objective is area control, but within the area you control you must place your workers to gain resources. In The Taverns Of Tiefenthal each player places their workers (dice) in entirely independent areas, and no player can steal a placement from another player -- but they can draft workers that the other players want, and even without interference, no player can take all possible actions in a given round, because their workers are limited. In Lords of Waterdeep all areas are jointly shared, and play is strictly first-come-first-served drafting.
Worker placement games tend to take constant planning, keep competition at a high level, and are usually medium to high complexity games. While most board game fans will be familiar with worker placement games, they often take longer to learn, longer to play, and require more serious play and less socializing -- although this is far from universal.