Determine the type of buffer
The :set <option> command will show the value of an option. In the case of
:set buftype this is generally set to nothing. It's empty. This is because we're usually working with a normal buffer. The exception is the quick window. Generally, the buftype of the quick window is quickwindow. The help window also has its own buftype, help.
These values are used programmatically to help create features with vimscript.
See more with: :help buftype