Empirical results show that frequently the meaning of expressions used by students in expressing their understanding of subject matter does not correspond to the meaning of those expressions in the subject matter theory that the students are expected to learn. There is also often a lack of identity of meaning between the same students' use of the same expression from one use of the expression to another, in very similar contexts. The context gives a specific meaning to any expression. This variation in context and meaning is very central to the phenomena of teaching and learning. In educational research there is a need to differentiate between specific meanings expressed in conceptualizing subject matter, on the one hand, and concepts and meanings seen as parts of cognitive systems and social languages, on the other. The contextual character of the use of language is crucial to the understanding of teaching and learning and needs to be more carefully considered. The article is a discussion of the problem of varying meanings of language expressions in relation to major traditions of research, focusing on meanings and concepts within the field of learning and teaching.