A host is a computer that is accessible over a network. It can be a client, server, or any other type of computer. Each host has a unique identifier called a hostname that allows other computers to access it.
Depending on the network protocol, a computer's hostname may be a domain name, IP address, or simply a unique text string. For example, the hostname of a computer on a local network might be Tech-Terms.local, while an Internet hostname might be techterms.com. A host can access its own data over a network protocol using the hostname "localhost."
Host vs Server
The terms host and server are often used interchangeably, but they are two different things. All servers are hosts, but not all hosts are servers. To avoid confusion, servers are often defined as a specific type of host, such as a web host or mail host. For instance, a mail host and mail server may refer to the same thing.
While a server refers to a specific machine, a host may also refer to an organization that provides a service over the Internet. For example, a web host (or web hosting company) maintains multiple web servers and provides web hosting services for clients. A file host may provide online storage using multiple file servers. In other words, a hosting company hosts multiple servers that serve data to clients.