Confussion with Repositories
What does it mean for a specific software (application, desktop environment) not to be in the repository of a distribution?
I mean, I read some days ago that some distro (don't remember which) didn't have certain DE in its repository so it couldn't be used. But, is this so radical? If there is not, say, LXDE in the repository of the distro 'X', it means you will never, ever be able to use it on your distro? Or it means that that there in not a precompiled version of the app/DE/etc for the distro, but if you download the source and compile it you will be able to use it?
I'm a little confused with the repositories, so if anyone could give me some explanation (in addition to answering the questions above :)) I would deeply appreciate it.
Thanks for your help