A paradigm is the collected thoughts, or framework, that represents the current 'thoughts' of a particular scientific field. A paradigm can also be a set of ideas, a standard, or a perspective. Don't mistake paradigm with paradox!
The word is Greek in origin and means "example" or "pattern".
It might make more sense to think of the differences between paradigms. For example, the difference in thinking that a Western and Eastern medicine practitioner would bring to a case. Or, the paradigm shift that occurred as a result of the Copernican Revolution - from a Earth- to Sun-centric Solar System.
The opposite to a paradigm shift is termed paradigm paralysis. During a paradigm paralysis, researchers are unable to see past the current 'thinking' or refusal to see problems with the current model.