Ectoplasm

"... an unpleasant greenish substance left behind by certain ghostly beings ..."

- Filius Flitwick

Ectoplasm is a green substance left behind from some ghosts. This substance can be clean with a simple Ectoplasm-Cleaning Charm, learned in Second year Charms. The Stickfast Hex is known to produce a sticky imitation of this substance.

Behind the scenes
The Toad, a ghost appearing in the earliest drafts for Harry Potter and the Philosopher's Stone, left ectoplasm all over its classroom.

Appearances

 * Harry Potter and the Chamber of Secrets (video game)
 * Harry Potter and the Prisoner of Azkaban (video game)
 * Harry Potter Trading Card Game
 * Pottermore