Let's tip our toes into a definition

I really liked the brief overview by the General Teaching Council Scotland

The four sections on this website lead you to more in depth discussions of the 'Why's' for practitioner inquiry

I really like this quote from the Sage Research Methods site about Practitioner Inquiry: 

"Practitioner inquiry is about the practitioner, whether they're a teacher, a lawyer, a doctor, or a social worker thinking about their work in a very curious, but also a very systematic way."