Pal, jazzman, regularly seen in square (5)
I believe the answer is:
plaza
'square' is the definition.
('plaza' can be a synonym of 'square')
'pal jazzman regularly seen' is the wordplay.
'regularly seen' indicates alternate letters.
'pal'+'jazzman'='paljazzman'
The alternating letters of 'paljazzman' are 'PLAZA'.
'in' is the link.
(Other definitions for plaza that I've seen before include "Open urban square or public area" , "Public square or market" , "Sp. square, market-place" , "Public square, as in Spanish town" , "Town square (Sp.)" .)