Captures the victim (most likely)
Incacerata is a spell that presumably binds the victim, or disables them from walking in any other way. Harry Potter tried to cast this at Severus Snape while he ran away from Hogwarts Castle after the murder of Albus Dumbledore, but the professor deflected it easily. 
"Incacerata" comes from incarcerate, which means "to capture."
Behind the scenes
- This spell is probably related to Incarcerous and/or Incarcifors.
- This spell may be the same as Caught!.