Creep in soil is pretty much similar in concept to creep in general. Only the manifestation and consequences are different in different materials and can be very peculiar in soil.
Creep in soil is the time dependant development of shear strains and/or volumetric strains in a soil mass in the state of a constant effective stress for a prolonged period of time.
It is also sometimes referred to as the gradual loss of cohesion over a prolonged period of time in soil.
Unlike concrete, where creep results in deflection and cracking, creep in soil to may lead to long term settlement, movements of slopes, gradual loss of soil from slopes or shear failure.