Butane is a gas. Factories press it into a liquid so it can sit in a small metal can. When you let it out, it becomes gas again and burns. People use it for cooking and heating: camping stoves, portable burners, some heaters. In Taiwan you meet it in cassette-stove cans, and also in cigarette lighters, which burn the same gas. It has no colour; a smell is usually added so you can notice a leak. The name is chemist-talk: but- means “four carbons,” and -ane is the ending for this family of simple carbon gases. A long way back, that but- piece is the same stem as the sour acid in rancid butter — so butane and butter are distant relatives, though actually nobody is cooking with butter-smell in the can. City pipe gas is mostly methane, a different gas; propane is a close cousin, also sold in tanks.