Aside from druids and bards, the third kind of Celtic wisdomkeepers according to the ancient tradition consisted of the seers, or ovates. Classical writers referring to the Celts of mainland Europe indicate that seers, bards and druids were three distinct communities; while in other areas these categories may have been more integrated. For example in Ireland we find the tradition of the filidh, or visionary-poets — a kind of wisdom keeper who combines the qualities of bards and seers.
What makes a seer? Begin with the word itself: one who sees. So the seers were the visionaries, the mystics and psychics who were able to receive information from the otherworldly realms.— Carl McColman, 366 Celt