We consider the question of the concepts of entropy and temperature in arbitrary nonequilibrium conditions in the framework of the so-called Informational Statistical Thermodynamics. This is the approach to Thermodynamics based on the statistical-mechanical foundations provided by a Gibbs ensemble-like algorithm in nonequilibrium situations. The resulting nonequilibrium temperature-like variable dubbed as quasitemperature - is shown to be a quantity measurable with appropriate 'thermometric devices'. A comparison of quasitemperatures that arise in different approximated nonequilibrium statistical-thermodynamic descriptions of the dissipative system is done. The validity of these different approximations is evaluated, and (in the framework of the theory) generalized Gibbs, Clausius, and Boltzmann's relations, as well as properties of the corresponding entropy-like function (or informational entropy in Jaynes-Shannon sense), that the theory introduces, are presented. Conceptual and physical aspects of the question an also discussed, and a partial comparison of these concepts with those arising in other approaches to irreversible thermodynamics is briefly attempted.4741921937964