In the
boat form of cyclohexane and related structures there are two ring atoms lying out of
the plane of the other four; exocyclic bonds to these two atoms pointing in a direction
roughly parallel to that plane are called bowsprit, the other two are called
flagpole.
Source:
PAC, 1996, 68, 2193
(Basic terminology of stereochemistry (IUPAC Recommendations 1996))
on page 2201
