The Banishing Charm sends an object away from the caster; the target object is said to have been Banished. The Banishing Charm is considered to be the reverse spell to the Summoning Charm (GF26).
References from the canon
Harry and his classmates practiced this spell in their fourth-year Charms class. Flitwick found himself being Banished around the room by Neville, whose aim wasn't very good. Can be a dangerous spell when heavy objects start flying away, so Flitwick had them practice on cushions:
He, Ron, and Hermione were sitting at the very back of the Charms class with a table to themselves. They were supposed to be practicing the opposite of the Summoning Charm today - the Banishing Charm. Owing to the potential for nasty accidents when objects kept flying across the room, Professor Flitwick had given each student a stack of cushions on which to practice, the theory being that these wouldn't hurt anyone if they went off target. It was a good theory, but it wasn't working very well. Neville's aim was so poor that he kept accidentally sending much heavier things flying across the room - Professor Flitwick, for instance (GF26).
Seems to be a milder form of the Knockback Jinx and the Repelling Spell.
The incantation, Depulso, comes from the video game version of Prisoner of Azkaban. As such, it's canonicity is questionable. The term is derived from Latin "depulsio" - "to drive away or repel."
From the Web
"Banishing Charm" from Harry Potter Wiki