There are, in Magic: The Gathering, an absolutely overwhelming number of subtypes. Subtypes are ways for the game to make meaningful mechanical information on the type line of the card, and, if you’re wondering, by volume, most of those subtypes are creature types. It’s how you get Humans and Wizards and Orggs and Kor and Brushwaggs.
But it’s not just creatures with subtypes; artifacts have them as well, with subtypes like blood and clue for the widely available tokens, but equipment is probably the best known. Enchantments similarly have Auras, as their most common subtype representative, but they also have things like Backgrounds, Shards, Sagas and Curses. Lands, well, the subtypes of lands are widely known, what with Plains, Island, Swamp, Mountain and Forest.
When you look to the instant and sorcery, subtypes are much less common. There’s Arcane, the Kamigawa era mistake, Adventures, which are from the mistake Eldraine, Lessons from Strixhaven about which I have no hot takes, and finally, the subtype Trap.
Traps are a little orphan subtyle from Zendikar and Worldwake, and that’s it. There are twenty trap cards, distributed almost evenly across the colours, and the mechanic is, to say the least, unsupported. There are two cards that relate to traps, one that tutors one up and one that makes your opponent discard them, and they’re both blue, which seems a foolish thing to me, but whatever.
If you’re not able to intuitively glean it looking at it, traps are a card that do something, and have an alternate, reduced cost, based on your opponent doing something that makes the trap even more effective. One of them, Mindbreak Trap is a legacy sideboard card because it can protect you from storm decks going off on turn one, and storm players will often delay an explosive turn to check for it (or any of a number of other possible explosive solutions). Beyond that they’re a category of card you’re most likely to see as someone’s pet.
Trap is almost what I’d consider a dead subtype; there are only so many applications of the flavour, and the mechanic, while nice, eats a lot of space on the card. Plus, the more complicated the trigger, the less room you have for the effect on the card. They want to be responsive, as well — it’s not like Guerrilla Tactics where the card is a basic burn spell that can also punish an opponent doing something to try and stop you.
Still, there’s a lot of room for flavourful play around the whole question of them: there could be creatures that react to traps, or that can be sacrificed to counter traps. There could be trap cards that recur themselves when their conditions are met, and there could be trap cards with an entirely different structure, and all that needs to link them together is ‘being a trap.’ Consider a Foretell card with rules text like ‘Foretell 4RR. This costs 4R less if an opponent gained life this turn.’ It’s still sitting out there, you did foresee the problem, but the spell itself doesn’t necessarily need to consume a ton of space on its alternate cost because a lot of that rules text is shuffled under Foretell. Then, the only thing that you need to do to make the card work with the other trap cards is to have the subtype.