Crown Block Guide In Oil & Gas Rigs
The Crown Block is one of the rig components (hoisting system) composed of a fixed set of pulleys (called sheaves). The location of this stationary block is mainly at the top of the rig derrick or drilling mast, where the drilling line is threaded.

The companion blocks to these pulleys are the traveling blocks.
https://www.drillingmanual.com/crown-block-oil-gas-rigs/