From WordNet (r) 3.0 (2006) [wn]:
catwalk
n 1: narrow platform extending out into an auditorium; "models
displayed clothes on a catwalk at the fashion show"
2: narrow pathway high in the air (as above a stage or between
parts of a building or along a bridge)
From The Collaborative International Dictionary of English v.0.48 [gcide]:
catwalk \catwalk\ n.
1. A narrow walkway projecting from a stage into the seating
area of a theater; it is used, e. g. by models displaying
clothes on it at a fashion show. Called also runway.
[WordNet 1.5 +PJC]
2. A narrow walkway high in the air to allow workers access
to parts of a structure otherwise difficult to reach.
Catwalks are located, e.g. above a stage in a theater,
between parts of a building, along the side of a bridge,
on the outside of a railroad car, on the outside of a
large storage tank, etc.
[WordNet 1.5 +PJC]