Metres square is the number of square metres in an area that is square in shape.
Square metres is the number of square metres in an area of any shape.
It's unfortunate that manufacturers of area cover products, from paint to lawn seed, have started using the symbol m2 on their packaging. This should be interpreted as the first explanation, when they actually mean the second. Alas, it's probably too late now to get them to change.
Oh dear, I've been mistaken all my life.
I always thought metres square meant something else.
10 square metres is 10m�.
10 metres square is a block of 10m X 10m = 100m�