I'm going to have an exam from methodology:(
It's not relly clear what is meant here, but a prop is a support - so it presumably refers to the different ways teachers can support students in their learning. But as "supporting students in their learning" is the teacher's job, it could refer to just about everything you do in the classroom, from the way you decide to structure the course and lessons, to the small details of how you conduct the lessons.
It could also be seen negatively of course - referring to students who become over-dependent on the teacher. Can you perhaps give us some more details as to exactly what the question is which you need to answer?
to Susan: I'm similar opinion like you that a "prop" can be a kind of supportive teacher.The problem is that my lecturer made a list of some exam questions and this was one of them-teacher as a PROP. I've got some good books in this subject like :Harmer "The practise of English language teaching" , books of Ur and others but I can find it nowhere.:((
I've never met it in a book, but you obviously know what a "prop" is, so you know enough to write the essay - discuss the possible meanings of "prop", and different kinds of support a teacher can offer. In conclusion, you could emphasize that props can break and/or bend, and that a teacher needs to know when to stop giving support and let students 'do their own thing'.