In America, "docent" usually refers to museum guides. Frequently volunteers and often retired, they receive varying amounts of training and may give scheduled tours or be available for drop-in touring. Docent quality varies wildly; we usually said no to docent tours when I was small because they were frequently so boring. I think this results from lack of training, though. At the Oakland Museum of California, the docents take university-level courses and are very educated in their specialties. A number are retired teachers or professors, and they're usually very popular with the schoolkids who make up most of the touring groups.