Lava

Lava is a naturally generating resource found in occasional above-ground pools and underground pools. Items thrown into it are lost forever, and players and mobs who fall into it lose 5 health per second.

Uses
Lava can be used to discard any unwanted items, and can be collected in a Stone Bucket to create a Bucket of Lava, which can be used to create traps, used in a Cooker to temporarily increase cooking speed, and used as decoration.