In the context of the TLS, a Concept is a label for a set of Words that have a role in the semantic field which they together define. A Word here is a subset of all the meanings a Character can have, that is, the one meaning that is actualized by being grouped together with the other Words under a given label. Sometimes there is a definition for the Word as such, but in most cases, a specific meaning is given for each of the Syntactic Word that are enumerated for a given word.
In addition to the way this group of Words contribute together to the semantic field of the Concept, the Concept derives its semantics from a definition and by its place in a Taxonomy of Concepts.