What is the difference between a teacher and a tutor?

This is a common question. A tutor is someone who know the content and helps the student master the subject. For example, a university student studying mathematics can assist a high school student informally because he or she knows the subject area. However, a tutor might not know how to sequence concepts or how to devise good tests or have enough experience with a variety of learners to make good guesses as to why the learner is struggling with a concept. Teachers, on the other hand, have knowledge of the learning and teaching process, in addition to subject matter knowledge.
When it comes to English language teachers, we assess the students’ level, make wise choices about the subject matter (which areas of grammar, what type of reading assignments, which kinds of listening exercises) as well as choosing exercises that match the student’s learning goals.
Thinking about traditional settings like schools and classrooms, teachers organize material for learning, conduct initial, ongoing and final assessments, set lesson objectives, provide instruction, organize meaningful review. Informal tutors help with the subject matter but usually within an overall curriculum or learning path designed by a professional.
In short, tutors “help with English” whereas teachers provide the whole classroom experience. We assess learner language and skills, help the student identify reasonable goals and the path to get there, choose exercises and assignments that are connected those goals, and can adapt as needed along the way.