Block:

An assembly of pulleys on a common framework; in mechanics, one or more pulleys, or sheaves, mounted to rotate on a common axis.

The crown block is an assembly of sheaves mounted on beams at the top of the derrick.

The drilling line is reeved over the sheaves of the crown block alternately which the sheaves of the traveling block, which is raised and lowered in the derrick by the drilling line.

When elevators are attached to a hook on the traveling block and drill pipe latched in the elevators, the pipe can be raised or lowered.

See crown block and traveling block.