Within the world of technology and computer science a “Client” is an edge Node on a network that requests and fetches data from a server.
Client is also the term used to distinguish between variants of software; an example of this is the client that is used to communicate with the Ethereum network. Ethereum can be communicated with though the following clients; GETH, Ganache, Parity and CPP-Ethereum, etc. Within blockchain the term client simply means and node/device that is capable of running the necessary software to parse and verify activity on the blockchain.