There are three types of slump that may occur in a slumps test, namely, true slump, shear slump and collapse slump.
True slump refers to general drop of the concrete mass evenly all around without disintegration.
Shear slump indicates that the concrete lacks cohesion. It may undergo segregation and bleeding and thus is undesirable for the durability of concrete.
Collapse slump indicates that concrete mix is too wet and the mix is regarded as harsh and lean.