Torpor

Torpor is a state that vampires can enter in Vampire: The Masquerade and Vampire: The Requiem. Basically, it amounts to falling into the vampiric equivalent to a deep sleep, like the one you have during the day.

Depending on circumstances, torpor may be the result of injuries or a voluntary process. The former is probably the kind of torpor you'll end up in, after you fuck up and get your lungs lined with lead by some Hunters or charred by a Mage or whatever; the latter is usually the result of an Elder deciding the world's too boring as-is and going to sleep until things become fun again. Either way you're basically a helpless, unconscious, mummified-looking corpse for the duration, though if you're seriously powerful (Methuselah and above, usually) you can maintain some degree of consciousness and even use some high-end Disciplines while in torpor.

Most Methuselah and above tend to be in torpor due to their need to feed on other Kindred's blood; one of them waking up is usually a very bad sign, as that fun week in Bangladesh might attest.

Meta

Exactly how long you stay in torpor (wilful or injury-caused) is dependent on your Humanity/Path of Edgelightenment rating; if you're max humanity it can be as little as a day, while lower ones have to stay crashed out for decades or centuries. Once you've run down the timer, you need to spend a blood point to try and get out of bed. If you're successful, you're awake but basically crippled and will need to hunt something double-quick.

In Requiem, entering Torpor also causes your Potency, or Power Stat, to decrease at a rate of about 1 point for every 10 years spent asleep. Now, you might be wondering "why the fuck would you want to lose Power Stat points?!" but here's the thing. Firstly, unlike in Masquerade where Generation is fucking hard to raise, it's way easier to boost Potency in Requiem - you literally gain 1 Potency per 50 years you've been active as a vampire. Secondly, raising Potency results in downsides - most notably, it means you eventually can only feed on other vampires (though in 2e you can take Merits to let you feed on other supernatural creatures; good in crossover games, not so good if the Storyteller won't let it happen). So spending time in Torpor usually is the lesser evil compared to becoming restricted to vampire blood, which raises all kinds of problems even if you resist the urge to commit Diablerie.