The general definition of enquiry would along the lines of asking something, so I would say an enquiring practitioner would be someone who is constantly questioning their practice. It can also be explained as some sort of investigation. This can be carried out alone or with colleagues and is extremely beneficial so teaching as it means constant improvement. By constantly questioning our own practice we will then be able to identify areas of improvement so that we can be the best teachers possible.
Practitioner enquiry has many benefits as well as development of own practice, it can empower teachers and give them control over what they teach and this can be very motivational. It also means that we can go further than just the classroom, practitioner enquiry could eventually change and improve the whole education system. This is due to the fact that it is highly adaptive and questioning is greatly encouraged by both pupils and teachers.
Personally I would say that working collegiately is a great was to improve the system of practitioner enquiry because teachers then have a chance to consolidate ideas and come up with the best solution which may lead to greater improvement.
It can allow us to come up with different teaching strategies based on strengths and weaknesses in past lessons. It gives teachers a wider knowledge base due to questioning and being critical. This is beneficial because if teachers can improve their own knowledge base then that means that there is far more knowledge to then be passed on pupils/colleagues.
A main challenge of being an enquiring practitioner would be taking criticism from others without getting offended and having the ability to criticize friends without feeling emotionally attached.