Page about leisurely walk in introduction (8)
I believe the answer is:
preamble
'introduction' is the definition.
(preamble is a kind of introduction)
'page about leisurely walk' is the wordplay.
'page' becomes 'p'.
'about' becomes 're' (common abbreviation for 'with reference to').
'leisurely walk' becomes 'amble' (I've seen this before).
'p'+'re'+'amble'='PREAMBLE'
'in' acts as a link.
(Other definitions for preamble that I've seen before include "Introductory or opening statement" , "Preliminary or introductory statement" , "Make introduction" , "Opening words" , "Introductory part of document or law" .)