Backend services are services that run behind a webserver and provide data that is used to build responses to the browser. The most common type of backend service is a database that stores information. When a request comes in from the browser that requires information from the database or other backend service, the server-side script connects to the database, retrieves the information, formats it, and then sends it back to the browser. On the other hand, when data comes in from a web request that needs to be stored in the database, the server-side script connects to the database and updates the data.