In teaching literature for high school and university and in journals for physics education, there are a few cases where one physical quantity is used in an ambiguous way. So, there is not one opinion about the meaning of the weight. In the same time there is not defined interpretation of energy-mass relation. Especially, there is a waste discussion to use or not to use the rest and relativistic mass concepts.
In this paper this problem is treated and our opinion about it is expressed.