A spell in the Harry Potter series that cuts the
target several times like a sword. It was invented by
Severus Snape and chronicled in his annotated Potions schoolbook, where Harry Potter learned it. The cuts can only be healed immediately after infliction by a countercurse also created by
Severus Snape.
The spell is ineffective on Inferi or other creatures who do not have or need blood.
The name derives from the Latin sectum, "cut", and semper, "always"