Definition: The edge of an RC tire that fits onto and sits on the wheel is the tire bead. There is sometimes a groove along the edge of the wheel into which the tire bead fits.
When gluing tires to the rim, the tire glue is placed along the rim where the tire bead sits and it is the tire bead that is actually glued to the wheel. With beadlock rims, there is a ring that is screwed to the rim and it holds the tire along the bead (hence the name).