1. The practice of a theory or skill.
2. Convention, habit, or custom.
Etymology: from Latin praxis, practice, exercise, action.
So how is 'praxis' different from 'practice'? As far as I can tell, the difference is slight. Praxis is more...intellectual; it's related to the philosophy of putting something into practice, whereas 'practice' is just about doing the thing. The term is used in religious philosophy to describe a combination of reflection and action.
'Praxis' is also the name of an American teacher certification exam.