The term cloud is used for some substructures of superclusters, an example being the Canes Venatici Cloud, which encompasses multiple galaxies. The exact phrase galaxy cloud is likely seldom used with this meaning though such names imply its existence: perhaps the term cloud of galaxies would have been clearer. Such structures (with cloud in the name) might be considered a galaxy cluster or might incorporate more than one or be a portion of one. The nomenclature is not universally consistent, and perhaps is evolving. (I speculate the name cloud generally arises from nebula-like appearances at some point in the object's observation history.)
The term galaxy cloud occurs with other intended meanings. It is occasionally used for clouds within a galaxy such as a molecular cloud. Also, the unusual names of the Magellanic clouds incorporate the term cloud as if it were a synonym for galaxy: I doubt they are ever referred to as galaxy clouds but a reader might mistakenly infer that as the meaning of the phrase galaxy cloud.