In IT and web systems. There are almost always 2 main entities. The SERVER and the CLIENT.With websites, the web server gives pages requested by a web client. Often when web designers use the term client, they are typically referring to a web browser type, a piece of hardware or the end USER of the website.An email client referred to the software used to collect and manage emails for a user. Examples include Microsoft Outlook, Thunderbird, Entourage and mac's mail.