I'm not tutor of English but I will try say in my point of view. Travel Agency: an agency engaged in selling and arranging transportation, accommodations, tours, and trips for travelers, a business that helps to make arrangements for people who want to travel. Tour: 1- Tour is a trip or journey for sightseeing or for entertainers to perform in many cities. 2- A trip with visits to various places of interest for business, pleasure, or instruction., 3- A group organized for such a trip or for a shorter sightseeing excursion. Company: 1. a number of individuals assembled or associated together; group of people. 2. a guest or guests: We're having company for dinner. 3. an assemblage of persons for social purposes. 4. companionship; fellowship; association: I always enjoy her company. 5. one's usual companions: I don't like the company he keeps. 6. society collectively. Unfortunately I'm not a native english speak so probably you need wait for a answer more correct

A "Travel Agency" is a specific term used to describe a company whose primary business is arranging trips. A "Tour Company" is a term which I have not heard of until now. It is perfectly understood, however, it does not have the specific connotation that "Travel Agency" does.