please help me understand what an extent is

[lostbackups]

I was just reading some technical documentation and realized I don't really know what "extent" means. I tried googling and searching the documentation but of course I can't simply find a definition and my search results are way off base for some reason. Can anyone here help me with the definition?

[foggy]

It is basically any repository that is a part of a Scale-Out Backup Repository.