Its like a big file that programs use to store things like settings.
But it is a seperate part of windows and has its own program to browse it (regedit). Also you can only use certain data types.
This is an example of a registry "folder"
quote:
HKEY_LOCAL_MACHINE\SOFTWARE\Patchou\MsgPlus2\RegisteredPlugins
Each "folder" can have different "keys" which are like files, and thats what your store data in.