100 square meters (3)
I believe the answer is:
are
'100 square meters' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for are that I've seen before include "(They/you/we) exist" , "Exist; square measure" , "live" , "(We/you/they) exist" , "Is, in the plural" .)