What is the difference between a dental resin filling and a dental composite filling?

In the strictest sense of the term, Dental Resin fillings will refer solely to the methacrylate component of the filling material (eg. Bis Phenol GMA).

However, it is rare to see an entire filling composed entirely of the unfilled resin material.

In practical terms, almost all resin fillings are in fact composite fillings (sometimes called composite resin or resin composite fillings). These fillings are composed of filler particles to provide color, fluoresence, and wear resistance suspended in a resin matrix.

Hence, from a technical view point, resin fillings will be composed of only resin (normally methacrylate or similar), while a composite filling will be composite of filler particles, suspended in a resin matrix. In practical terms, there will really be no difference. When your doctor places a resin filling, or composite filling, you will be getting a composite resin filling.