Accio
A spell to bring an object back into your hand. It can be used to bring a certain object, such as in Accio Butterbeer.
Alohomora
This spell opens a locked or closed door. The opposite of this is Colloportus.
Avada Kedevra
One of the three Unforgivable Curses, this spell causes death.
Colloportus
This spell locks a door shut. Hermoine uses this to cover their escape at the end of Book 5.
Crucio
One of the three Unforgivable Curses, this spell is the Cruciatus Curse and causes great pain. Umbridge tries to cast this on Harry at the end of Book 5.
Diffindo
The spell used to rip open tapestries and such. Used quite a bit in the computer game based on Book 2.
Expecto Patronum
This spell creates a silvery protective creature, a patronus. Harry’s patronus is a stag; Cho’s is a swan. Hermoine has an Otter.
Expelliarmus
One of the more simple spells, and the first spell that the D.A. group works on in Book 5. This disarms your opponent.
Finite
A spell to cancel the effects of another spell. Lupin uses it on Neville to get him to stop dancing at the end of book 5.
Flagrate
A form of fire spell, Hermoine uses this to mark an “X” on doors in the Mysteries area in book 5.
Flipendo
A simple spell that flips something over.
Impedimenta
This spell causes a person to freeze for about a minute.
Imperio
One of the three Unforgivable Curses, this allows a wizard to take total control of another person.
Impervius
A spell to cause an invisible wall to form. Quidditch players use this to keep the rain off their faces at times.
Incarcerous
Umbridge tries this on the centaurs in book 5 - to wrap ropes around them - but the centaurs easily shake them off.
Incendio
A spell to cause a fire to burn.
Legilimens
A spell to extract memories and feelings from another person, to in essence look through the memories another has.
Levicorus
A nonverbal spell to hang a person in the air by one ankle.
Locomotor
The locomotor spell causes something to move in a given direction. For example, to move trunks along with you, you would command Locomotor trunks. To cause someone to freeze stiff, you use Locomotor mortis.
Lumos
This spell causes the wand tips to glow and give off light.
Morsmordre
A dark spell that causes a dark mark - the sign of Voldemort - to appear.
Muffiato
A spell that fills the ears of anyone nearby with buzzing, so that conversations are not overheard.
Nox
A spell to cause darkness, the opposite of Lumos. Interestingly, the name of a fun computer RPG.
Obliviate
A memory erasing charm that Professor Lockhart was extremely fond of.
Petrificus Totalis
A spell to cause someone to freeze completely. It seems there are several different spells that cause this same effect :)
Portus
The portus spell creates a portkey that allows people to move from one destination to another easily.
Protego
A spell of protection, to ward off magical attack. Harry uses this at the end of Book 5 to keep a sphere that another is casting “Accio” on.
Reducto
An assault spell, reducto causes damage to what it is fired at. The students use Reducto to blow apart bookshelves at the end of Book 5.
Reparo
A simple spell to repair an object that is broken.
Riddikulus
An anti-boggart spell, that causes the boggart’s scary shape-changing ability to be mediated. Mrs. Weasley has trouble with this one at the beginning of Book 5 when a boggart torments her with sights of her family dead.
Scourgify
A cleaning spell, James uses this on Snape when they are young to clean Snape’s mouth out with soap.
Silencio
A spell to cause something (or someone) to become silent. As Hermoine instructs Ron, this spell is done with a sharp jab of the wand, not a wave.
Stupefy
This spell should freeze an object in place, but when Umbridge tries to use it on an escapee firework, it explodes instead.
Tarantallegra
A Death eater uses this dance-causing spell on Neville during the final battle in Book 5.
Wingardium Leviosa
Harry uses this to levitate tentacles away from him at the end of book 5.