Burning

Burning is a debuff inflicted when the player comes in contact with Hellstone, Hellstone Bricks, or Meteorite. The player takes continuous damage and has their movement speed reduced until they step off the block. Damage is taken at a rate of approximately 50 points per second.

The debuff can be prevented by equipping any of the numerous derivatives of the Obsidian Skull, allowing the player to step on any of the three blocks without taking damage.

Trivia

 * The debuff was created for the sole purpose of preventing Hellstone abuse, where the player would voluntarily take direct damage from Hellstone and use the invincibility frames as immunity from higher damage sources, such as lava or a Hardmode boss.
 * Prior to 1.3.0.1, all biomes that contained blocks that inflict this debuff had the same music as a Blood Moon.