An Enchantment is a spell, mostly used in fantasy games that follow the concept of spells.
It's a 'positive' spell targeted on friendly targets. When these spells are cast they mostly have a 'longer' effect on the target.
(eg. an invisible shield that lasts for 15 secondes and decreases incoming damage by 10)
Of course these Enchantments can vary in much ways and types.
Warrior: Damn duud I'm under attack by a creature.. I'm dying !!
Healer: dunt worry, I'll cast an enchantment for you