International business can be looked at two ways. One way is whether a specific company buys and sells solely within the boundaries of its own country for domestic business or whether it also buys and sells to other countries. If it does both, buying and selling domestically and with other countries, it is said to be and described as an international business. IBM is a good example of this use of the term. IBM does not just buy and sell within America, it buys and sells to other countries. It is described as an international business. The second way has to do with the activity of buying and selling to other countries. For example, when IBM--which is an international business company--buys and sells to other countries, it is engaged in and doing international business by buying and selling on an international level. So "international business" can be used (1) to describe a company (e.g., It is an international business company), and it can be used (2) to talk about an activity of a company (e.g., They do international business by buying from and selling to China and India and Burma and Australia).
I wonder if there isn't more to your question than this. International business is simply business that is done between countries or between firms in different countries. It can be an instance where a firm in one country buys from a supplier in another country or it can be an instance in which a firm has operations in many different countries. This is a fairly obvious answer, though, so I wonder if there is more to your question.