A sorcerous spell that prevents anyone from teleporting either into or out of (and often both) a given area.
The range of a teleport block depends on the power of the sorcerer casting the spell.
A teleport block will typically cover only a few hundred square yards; however, a truly powerful wizard such as Loraan may be able to place a block that covers several square miles. (A square mile is 640 acres, and an acre is 4840 square yards.)
A sufficiently powerful sorcerer or wizard may be able to break through a teleport block. (Daymar has done this on occasion, as has Sethra Lavode.)