Held a conference about a measure (5)
I believe the answer is:
metre
'a measure' is the definition.
(metre is a kind of measure)
'held a conference about' is the wordplay.
'held a conference' becomes 'met' (I've seen this in another clue).
'about' becomes 're' ('re' means regarding or about).
'met'+'re'='METRE'
(Other definitions for metre that I've seen before include "Approx. thirty nine point three seven inches" , "Beat pattern (mus.)" , "Poetic rhythm" , "Yard is smaller than this" , "Unit of length in metric system" .)