The Stunning Spell (Stupefy) is an offensive that stuns the target, knocking the victim backward and ragdolling them for a short amount of time. This stun spell is decent for offensive purposes due the short duration of time used to type the incantation.
"Stupefy" comes from the Latin word stupere, meaning "to be stunned." Stupefy is also an English word, which means "to stun" or "to amaze."
The Stunning Spell's short duration may be countered using the Reviving Spell, Rennervate.