Existing Wording
The usability of the codes is closely linked to the quality of the definitions. Although a definition is not required for each concept, a good definition SHOULD be provided. In the absence of any definition, there is no formal meaning associated with the concept

Comments
If we are going to allow a value set to define its own coded concepts outside of a containing code system that provides semantics for the concept it may be wise to require that a definition MUST be provided for these codes. This way the intent of each of these codes is appropriately considered and communicated.

Grahame's Comments
there are lots of codes out there in the real world that don't have definitions. On the other hand, the shareable value set profile should make definition mandatory. Which will be a problem for HL7 because HL7 has many codes with no definitions