Catline is a line powered by the cathead, which is a concave, rotating, pulley-type device mounted on the end of the cat shaft of the drawworks. Catlines are used to lift or pull equipment around a rig.
Source: API RP 54, Recommended Practice for Occupational Safety for Oil and Gas Well Drilling and Servicing Operations, Third Edition, August 1999 (2007). Global Standards
A rope, usually reeved on a crown block sheave in a derrick or mast, for the primary purpose of lifting and transferring materials from one place to another about the derrick or mast floor. A rotating cathead imparts the pulling power to the catline that is wrapped on it.
Source: Petroleum Safety Orders–Drilling and Production, Definitions, California Code of Regulations, 8 CCR § 6505, December 2012. Regulations