"Depulso! . . . She always was too grand for her own good. There’s no turning back now."
-- Severus Snape while banishing Dolores Umbridge (CC3.9)
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:
Seems to be a milder form of the Knockback Jinx and the Repelling Spell.
Severus Snape used the spell on Dolores Umbridge in an alternate universe set up by the Experimental Time-Turner (CC3.9).
Derived from Latin "depulsio" - "to drive away or repel."
The incantation, Depulso, first came from the video game version of Prisoner of Azkaban. As such, it's canonicity was questionable, but the inclusion in The Cursed Child during Snape's tussle with Umbridge brought it into the canon.
From the Web
"Banishing Charm" from Harry Potter Wiki