  We review the role of Gibbons-Tsarev-type systems in classification of
integrable multi-dimensional hydrodynamic-type systems. Our main observation is
an universality of Gibbons-Tsarev-type systems. We also constract explicitly a
wide class of 3-dimensional hydrodynamic-type systems corresponding to the
simplest possible Gibbons-Tsarev-type system.
