Explain Linux kernel state terminology e.g. net.next, linux-next, net.git

Most of the top-level kernel development happens not on github but on git.kernel.org.

See http://git.kernel.org/ for a list of repositories.

net.git is David Miller's kernel tree.

You can obtain it like this against your own local tree :

git remote add net git://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git
git fetch net

net-next.git is the tree that contains all patches that will be submitted to Linus for Next kernel merge window.

Is there a page that documents or can someone explain the meaning of these items in context of the Linux kernel?

You can have an overview of all kernel's tree on kernel.org

linux-next in short words is a git tree that is the merge of all of the developer and maintainers trees. You can view all different trees included here in ./Next/Trees