Taken from here: https://stackoverflow.com/a/171558
let g:clipbrdDefaultReg = '+' mean?
Plugins are configured via global variables, defined in your
~/.vimrc. As this file is read before any plugins are loaded, this is a convenient way to configure plugins.
Most plugins prefix those variables with their name (
g:PluginName_ConfigVar); this plugin is old and does not, but @mMontu found it nonetheless: clipbrd. Usually the plugin page (or the initial comment block at the top of the script) has an explanation of the config variables and possible values.
If you don't have a
plugin/clipbrd.vim file in your
~/.vim/ folder, you can safely drop this line.