Backend in web development is the "behind the scenes" of a software. While the frontend would be what's visible to the end users, the backend would be what administrators of a software see.
In the universe of Umbraco we refer to backend as “backoffice”.
The Umbraco backoffice serves multiple purposes in Umbraco. The best description of it is probably that it is the main control room of an Umbraco installation. Multiple workflows start here, especially content editing. During the initial setup of a site, you will see a lot of the backoffice.
Once a site has been developed and is handed over to the end user, the backoffice is where they will be doing their daily work. In most cases, this means creating new pages (called content nodes), updating existing content, uploading and inserting various media items such as images, videos, and other files.
Customizable user experience
The Umbraco backoffice can be customized to fit any need an end user might have. This is done by creating custom Document Types where you can easily build the user interface as you would like your end user to see it. This allows for customizing workflows for end users to allow them to work quickly and efficiently with their site once it has been handed over to them.
The backoffice allows you to give editors almost unlimited freedom when creating and editing content, or to restrict them to ensure that design guidelines, rules or procedures are being followed to the point.
Coding in the backoffice
It is possible to edit code directly from the backoffice. The markup of Templates, CSS, Partial Views and much more can easily be changed by logging in through any browser, if small changes are needed to be done.
We do recommend that most coding is done by using an editor made for the purpose, like Visual Studio Code, and that a Git repository is used to synchronize changes to the Umbraco installation. This allows for easier restore and debugging.