"A length of brinestalk wrapped in oil-soddened cloth."
When ignited and held in a hand slot, provides light for an orthogonal range of 4 and a diagonal range of 2.
Torches last for 5000 turns.
For most characters, torches are a tremendously useful light source, allowing you to travel at night or explore caves and buildings. Additionally, they make decent off-hand weapons, burning and potentially igniting opponents in combat. They are less effective than actual weapons, and provide no defensive bonuses, but being able to see where you're going is usually an indispensable benefit.
Lit torches can also be used to set flammable objects, like webs, on fire. Enemies usually take a few more hits to ignite.
Torches have some noteworthy drawbacks. They only illuminate a rather small area around you, putting characters who rely on long-distance attacks in significant danger. They also burn out after 5000 turns. All characters begin the game with a large stack of them, and they're cheap enough to easily replace, but weigh a lot.