A pre-coordinated term has a single code associated with it. A term may consist of one or more words. A well-defined collection of words represents a concept or thing.
For example, RadLex assigns the code RID1276 to the term left upper lobe bronchus.
A post-coordinated term has two or more codes that represent a collection of concatenated words. It concatenates preexisting terms to create a new concept. The concept is represented by a collection of concatenated codes ordered by when a word appears in the term.
For example, left and lung are preexisting terms. Concatenated, they become left lung, to which the National Cancer Thesaurus assigns it two codes, C25229 and C12468.
