When on, the builtin termcaps are searched before the external ones. When off the builtin termcaps are searched after the external ones. When this option is changed, you should set the 'term' option next for the change to take effect, for example:

:set notbi term=$TERM

See also termcap. Rationale: The default for this option is "on", because the builtin termcap entries are generally better (many systems contain faulty xterm entries...).

(default on)