What is it called when one computer can connect to another?

The term that best describes when one computer connects to another is "Networking." Networking refers to the practice of interconnecting computers and devices to share resources, communicate, and exchange data. This concept encompasses various methods and technologies that enable the linking of different devices within a system.

Connectivity, while closely related, generally refers to the ability of devices to connect to a network or the internet. It captures the aspect of being able to join a network but does not encompass the broader concept of the relationships and protocols that allow multiple computers to communicate effectively with each other.

Thus, networking embodies both the connection itself as well as the protocols, topology, and rules governing those connections and communications between computers, making it the most appropriate term in this context.