A Fellow is usually involved in teaching, but may simply do research; and in some cases a Fellow is a mature student. A college may also invite an overseas academic to come and just be 'in residence'; one could say that sort of Visiting Fellow was involved in teaching, but he may simply hold a few seminars.
So a Fellow is not just a Member. I, for example, am a Member of my college, but not a Fellow.
Student or Learner