Intercity means “between cities,” or “going from one city to another.” An intercity train or bus does not only travel around one city; it links one city with another. In some places people also say “an intercity” to mean that kind of train. It is everyday language for travel. Though actually, “city” here is used a bit loosely: a stop might be a big town, and much of the ride may be through the countryside. What matters is that the service joins cities, not that every minute is spent inside a city. Do not mix it with international, which is between countries, or with a city bus that never leaves town.