In technology, a client refers to a piece of software or hardware that requests information or resources from a server. Clients are typically used in client-server architectures, which are common in many computer networks and online systems.
A client is responsible for initiating a connection to a server, sending requests for information or resources, and receiving responses from the server. The client can be a separate piece of hardware or software running on a computer, or it can be integrated into a larger software application.
Clients can take many forms, including web browsers, email clients, chat clients, file transfer clients, and more. Each type of client is designed to communicate with a specific type of server, and can use different protocols and methods to do so.
For example, a web browser is a type of client that is used to request web pages and other resources from a web server. The browser sends requests for information using the HTTP protocol, and receives responses in the form of HTML, CSS, and other data.
Similarly, an email client is a type of client used to request and send email messages from a mail server. The client typically uses the POP or IMAP protocol to retrieve messages from the server, and the SMTP protocol to send messages to other email servers.
In some cases, clients may be designed to run on multiple platforms or devices. For example, a chat client may be available as a desktop application, a mobile app, and a web-based client. This allows users to access the chat service from different devices and platforms, while still communicating with the same server.

Bitcoin Core: This is the official full-node client for the Bitcoin network. It allows users to store and manage their own copy of the Bitcoin blockchain, and to make transactions on the network.
Ethereum Mist Wallet: This is the official client for the Ethereum network, it allows users to store, manage and make transactions on the Ethereum network. It also allows users to interact with decentralized applications (dApps) built on Ethereum.
MyEtherWallet (MEW): This is an open-source, client-side wallet for Ethereum and other ERC-20 tokens. It allows users to generate and manage their own private keys and make transactions on the Ethereum network.

In the world of cryptocurrencies, a client can be thought of as a software application that allows you to access and interact with a specific blockchain network. Just like a web browser is a software program that lets you access and view websites on the internet, a cryptocurrency client lets you connect to a blockchain and perform various functions such as sending and receiving cryptocurrencies, viewing transaction history, and interacting with smart contracts.