Magic: The Gathering is the first and most popular collectible trading card game, released by Wizard of the Coast in 1993. Originally set in the fantasy plane of existence known as Dominaria and starring rare but godlike planeswalkers, those with the spark to travel between planes and summon (now copies of) monsters from there. It's expanded multiple times a year, even outsourcing its lore now with Universes Beyond cards from, for example, Warhammer 40,000. Only official white- or black-bordered cards without acorn stamps are valid in tournament play.
100-card singleton (only basic lands can have any number), 40-life, 4-player games are most popular. This format is called Commander, or Elder Dragon Highlander (EDH) originally. Your deck then has one legendary creature as leader in the command zone, costing 2 mana more for each time it has been cast from there, and can be returned to there if it c