means A series of words spoken or chanted as a magic spell or charm, often in ritual.

from From Latin incantare, "to chant a spell upon" — built from in- ("upon") plus cantare ("to sing"), the same cantare that gives us chant and enchant. The idea is older than the word: that singing or chanting words over a person or thing could work magic on them. So at its root an incantation is literally a song aimed at the world, sung until it obeys.