Client-Side versus Server-Side
Computer networks are broken down into two main areas: client-side and server-side. Average computer users work on the client-side. This is because their computers are referred to as "client" computers. When you are browsing the internet, think of your browser as the client. Now think of the webpage you're requesting as a file on the server (all webpages are made up of multiple files:
.css, etc. and are sometimes dynamically created using server-side scripts). You can find this webpage using a URL.
Programs or scripts that run specifically on servers are called server-side languages. Typical users will not be able to distinguish between these two different types of programs/scripts during their computer usage. Some examples of server-side programming languages (or backend languages) include: PHP, .NET, ASP, ColdFusion, C#, Visual Basic, Python, Java, and Ruby on Rails.