Positions of about fifty steps (6)
I believe the answer is:
places
'positions' is the definition.
(I know this)
'about fifty steps' is the wordplay.
'about' indicates putting letters inside.
'fifty' becomes 'l' (Roman numeral).
'steps' becomes 'paces' ('pace' can be a synonym of 'step').
'l' inserted into 'paces' is 'PLACES'.
'of' acts as a link.
(Other definitions for places that I've seen before include "Locations" , "Sites" .)