Accio, also known as the Summoning Charm, is used to make objects fly straight to the spell caster. It is usually used with an object name afterwards such as "Accio Sweets".
In Latin, Accio means "I call for", or "I summon".
This useful spell was first introduced at the beginning of Goblet of Fire, where Mrs. Weasley used it to get a large amount of Ton-Tongue Toffees that Fred and George were attempting to bring to the Quidditch World Cup. Hermione was the one who taught Harry the spell in order for him to complete the first task in the Triwizard Tournament where he wanted to summon his Firebolt in order to best and outspeed the dragon.
However, certain spells may be imbued on items to kept them from being summoned with a simple Summoning Charm.