The morning and evening meals are generally eaten outside of the company domain except for company get-togethers in the evening (which, depending on the company, can be frequent or infrequent). Lunch is eaten during business hours and because Korea has a group-oriented culture rather than an individual-oriented culture, the eating of lunch generally comes under the company domain.
Eating lunch together could involve going out to a restaurant, getting food delivered to the workplace or eating in a company restaurant if one is provided. The company, or possibly the senior manager, generally pays for the meals of all people in the group for those working at a company.
It is general practice for Koreans to eat together. Bringing a packed lunch is a practice which is becoming less and less common. Similarly, eating out as an individual or small group or taking care of personal business instead of eating together would be looked down on if done often. The team, department or whole company will eat together.
Eating together is seen as something that builds up group spirit. Any acts of individualism when group-behavior is expected will tend to get a person excluded from the group, which is a serious issue in a group culture like Korea.