In Everything core, a nodetype refers to type of node. Since everything in Everything is a node, every node has to have a title and nodetype to tell them apart.
For example, this node is an e2node which in turn contains a writeup; There's both user and e2node called WWWWolf (there may be different nodetypes with same title, that's the point).
If you install a raw new clone of Everything, the only nodes worth creating as a normal user are documents and images... unless you develop a new nodetype of your own.