What is the difference between 'concept' and 'assumption'?
These two terms are very dissimilar. The term 'concept' refers to an idea or abstract principle. For instances, force, space are concepts in Physics, God can be a method in religious beliefs, time is a method in Metaphysics, demand & supply are concepts in Economics, etc. However 'assumption' means a statement of something that has been taken for granted or something that has been accepted without any real proof.
For example, "people are maximizers" is an assumption in Economics.