A human suit
is a costume intended to disguise
one as a human being, or a different human being. It could be made out of fabrics, synthetic materials
, animal skins
, or, as in the movie The Silence of the Lambs
, human skin. There is also a reference of a human suit in Donnie Darko.
It could also be used as a rhetorical device to refer to the animal qualities of another. (i.e. He/She is like a ... in a giant human suit.)