Supercooled liquids are sometimes described as being composed of a mosaic of patches that may be listed in a “library”, each one having some form of non-periodic order. Looking closer, one finds this construction elusive. In attempting to give the notion of mosaic a precise sense, we find that we are inevitably led to the construction of a procedure for compressing the information in the particle configuration, essentially the same as that used for texts. The amount of stored information needed by an optimal encoding directly defines the configurational entropy. A solid, in this view, is a particle arrangement described by a low amount of information, that can only flow by breaking into uncorrelated pieces, thus increasing its complexity.