Definitions for "Bottom Bracket"
This is where the down tube, seat tube and chainstay join and houses the crank and crankset. It houses either an adjustable bearing or a cartridge bearing.
The mechanism at the bottom of the bicycle frame which holds the spindle and crank.
The bottom bracket is where the downtube, seat tube, and chainstays come together. A spindle passess through the bottom bracket, and the cranks attach to the spindle.