2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/18761The difference between the terms additivity and extensivity, as well as their respective negations, is critically analyzed and illustrated with a few examples. The concepts of subadditivity, pseudo-additivity, and pseudo-extensivity are also defined.Contribution to the Proceedings of the International School and Conference on Non-Extensive Thermodynamics and Physical Applications, Villasimius, Sardegna, Italy, May 2001. To be published in Physica AStatistical Mechanicstext