This is a person with special knowledge, skills and training. They transmit knowledge, develop critical thinking and prepare people. But unfortunately, there are very few of them left. Not everyone does this in good faith. For example, at university, I was forced to look for dissertation writing services, I used https://ca.edubirdie.com/dissertation-writing-services for this. All because the material at the university from the teacher was simply terrible. She was constantly late for lectures and turned a blind eye to everything. There should not be such teachers.