What does For Developers mean?

So recently Apple released an iOS 7 Beta version and it says "For Developers". What does that mean?
Can i get it for my iPhone 4?

No, it means only certain group of people, who developed the ios7 beta, can test it.

It means it has been released so software/app developers can start testing on the new OS so the app store will have tested and functioning apps to download immediately it is released to the public.

Beta means it's a late test version that essentially works, but still has some bugs in it. It's released early for testing by developers to determine software compatibility with the new version. That's why it's labelled "for developers."

If you want to install it, it's with the understanding that there's no tech support for it beyond bug reporting by the test teams and outside developers. If you run into a problem, you're essentially on your own, and the problem may be due to a known bug that's being worked on, so there might not be a fix for it yet. They don't want to deal with the deluge of people who don't understand that and whine about how bad the new version is.

If it's an open download, then anyone can get it and install it, but it's with the understanding that you use it at your own risk. If you manage to brick your phone, it's your problem, and your fault for ignoring the warnings. Some people are ok with the risk and the lack of tech support and just want to be the first kid on the block to preview the latest version on their device. If you aren't ok with that, stick with the final version releases.

Developer Beta versions are pre-release versions for testing & Bug finding.
After Beta Testing is Over Final version releases.

It is always better to have final version