Stock type of pen (6)
I believe the answer is:
corral
'type of pen' is the definition.
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for corral that I've seen before include "Pen for cattle in the US" , "Famous gunfight at the OK ..... in American West" , "Horse enclosure out West" , "Pen for cattle - ring of waggons" , "Ranch pen" .)