gvim (thing)

gvim is actually a part of vim distribution. It's really a superset of vim - it provides all the vim functionality and then some. gvim stands for GUI Vim.
Some of the additional features include:

• Scrollbars (horizontal and vertical) are provided.
• Mouse control and movement are supported (things like selection can be done with the mouse).
• Menus & Toolbars are provided for those of us who like eyecandy.

Because gvim runs as in X11 or in Windows it provides native methods of clipboard use. That is you can select stuff in X and expect it to be copied on middle mouse button click in other window. Basically gvim is just a prettier version of text mode vim.