The actual definition of professional behavior varies from industry to industry because each one requires something different of its professionals but, in general, a professional conforms to the technical and ethical standards of one's profession. There is a lot of room for interpretation in that definition, which is why it varies amongst different industries.
Despite the variances, there are some common principles an individual should abide by. Professional behavior includes behaving with integrity, honesty and good ethics. It also includes communicating with others in a respectful manner, showing initiative, meeting commitments and responsibilities, contributing and participating in team events, recognizing and learning from personal mistakes, being punctual and accepting responsibility for one's own actions.