"Host" and "end device" mean the same thing — any computer that connects to a network and participates directly in communication; it is where a message originates or is delivered.

Every computer on a network is called a host or end device. A host is either the source of a message or its destination: data originates with one end device, flows through the network, and arrives at another end device. Everything in between (cables, switches, routers) exists only to carry that traffic between hosts.

Examples: desktops, laptops, smartphones, tablets, printers, IP phones.

Go deeper:

• Host (network) (Wikipedia) — defines a host as a device that acts as source/destination of messages, and distinguishes hosts from infrastructure nodes.
• Key Players (Practical Networking) — frames hosts as the endpoints that originate and consume traffic, with everything else in between just carrying it.

A server provides information/services; a client requests them — and the same device can play either role depending on the exchange.

Server and client are roles in a conversation, not fixed kinds of hardware. A computer is a server whenever it runs software that answers requests, and a client whenever it runs software that makes them. That's why the same machine can be both at once — your laptop is a client when it browses the web, but a server when it shares a printer. What decides the role is the software running, not the box.

* Client and server are roles in an exchange — the client requests, the server answers — not fixed kinds of hardware. *

• Server: A computer that provides information or services to end devices (e.g., email servers, web servers, file servers)
• Client: A computer that sends requests to servers to retrieve information

Go deeper:

• Client–server model (Wikipedia) — spells out the request–response pattern (clients initiate, servers await/answer) with concrete examples.
• Key Players (Practical Networking) — goes deeper on hosts/clients/servers as roles rather than fixed hardware, and how they interact.