Speculation about everyone dancing (6)
I believe the answer is:
ballet
'dancing' is the definition.
(ballet is a kind of dancing)
'speculation about everyone' is the wordplay.
'speculation' becomes 'bet' (bet is a kind of speculation).
'about' indicates putting letters inside.
'everyone' becomes 'all' (I've seen this before).
'bet' going around 'all' is 'BALLET'.
(Other definitions for ballet that I've seen before include "kind of skirt" , "Art of the Kirov or Bolshoi" , "The theatre of dance" , "Theatrical dance" , "Nureyev's forte" .)