In this article basic concepts concerning "uncertainty" and their related topics are presented, explained using examples and discussed. Namely, the concept of "true value" underwent a significant evolution from the so called "Error approach" to the "Uncertainty approach". The concept of quantity value itself is consistent with the concept of uncertainty, rather than "exact value" presented by one exact real number. A particular schism with previous Czech terminology has been solved and some general rules for terminology are stated. This paper was supported by the Czech Ministry of Education, Grand agency INGO II, project LG13026. and Jan Obrdržálek.