These terms are used in the "Definition of a simple interpretation" table on <http://www.w3.org/TR/2004/REC-rdf-mt-20040210/#interp> . I am a little unclear on their meaning.

At this point I think they mean, Intermediate Language, 

I am a little unclear on the meaning of these abbreviations. I am guessing that they mean Intermediate Language, Intermediate System, and Intermediate Extension (or any of these, substituting "interpretation" for "intermediate"). This information isn't explicit in the documentation, and I don't have enough context to know conclusively what is being referred to.

**Edit** *I copied the section where it is used below:*

```
Definition of a simple interpretation.

A simple interpretation I of a vocabulary V is defined by:

1. A non-empty set IR of resources, called the domain or universe of I.

2. A set IP, called the set of properties of I.

3. A mapping IEXT from IP into the powerset of IR x IR i.e. the set 
   of sets of pairs <x,y> with x and y in IR .

4. A mapping IS from URI references in V into (IR union IP)

5. A mapping IL from typed literals in V into IR.

6. A distinguished subset LV of IR, called the set of literal values, 
   which contains all the plain literals in V

```