Charm is a spell that adds certain properties to an object or creature.
Levitation Charm causes an object to lift
Levitation (Hover) Charm
Colour Change Charm causes something to change colours
Colour Change Charm
Cheering Charm makes somebody happy
Cheering Charm
You have your mother's eyes. It seems only yesterday she was in here herself, buying her first wand. Ten and a quarter inches long, swishy, made of willow. Nice wand for charm work. - Mr. Ollivander Harry Potter and the Philosopher's Stone
We have received intelligence that a Hover Charm was used at your place of residence this evening at twelve minutes past nine.
Harry Potter and the Chamber of Secrets
“An Engorgement Charm, I suppose?” said Hermione, halfway between disapproval and amusement. “Well, you’ve done a good job on them.”
Harry Potter and the Chamber of Secrets
Engorgement Charm A spell which causes something to grow large.