Blue copperas

What is Blue copperas?

Blue copperas definition and meaning on Dictionary terms:
noun Chemistry, Mineralogy.
a salt, copper sulfate, CuSO4a??5H2O, occurring naturally as large transparent, deep-blue triclinic crystals, appearing in its anhydrous state as a white powder: used chiefly as a mordant, insecticide, fungicide, and in engraving.