The Collaborative International Dictionary of English v.0.48:

Lobster pot \Lob"ster pot\, n.
   a device used to trap lobsters, consisting of a
   semi-cylindrical structure made of wooden slats, with
   openings formed of funnel-shaped nets allowing lobsters to
   enter, but impeding their exit. It is also called a lobster
   trap.
   [PJC] Lobster thermidor

WordNet (r) 3.0 (2006):

lobster pot
    n 1: trap for catching lobsters