Seer is a term for a mortal with connections to the Otherworld. They're able to see and communicate with the dead. They can also "read the future" via tarot cards. They know about the Caster world, and are able to comprehend them but are unable to actually produce magic. However, in the example of Lennox Gates they also have the ability not only to read the future, but also to see it through visions.

Known Seers