The word "Internet" describes a digital connection between many networks or a network of networks. It is often believed to mean "International Network," but when the name was coined in the early 80s, people had no concept of how the Internet's size and scope would grow.
The very similar word "Intranet" should not be confused with "Internet." "Intranet" describes a network within a single organization. When these singular networks were expanded to connect to other networks, the connection was called an "Internet." A good comparison would be interstate highways that connect to many states, while intrastate highways stay within a single state's borders.
Soon, more networks and hosts were added to early incarnations of the Internet, and the name grew to describe the many networks connected throughout the world.