Thread:Support/About MediaWiki:Filejournal-fail-dbconnect/sv/reply

A back end is a system or component that ordinary users don't interact with directly and don't need to know about, and that is responsible for a distinct task or service - for example, a storage back-end is a generic system for storing data which other applications can use. (Conversely, the front end is what users interact with directly; this term is basically synonymous with "user interface").

Many times these definitions aren't followed exactly because this is the sort of jargon that managers and marketroids use when they want to sound as if they know what they're talking about.

I would translate back-end as "system" or "service", or (depending on context and language) even leave it untranslated. See also wikipedia:Front and back ends.