An
idea which is
bright, meaning;
smart,
intelligent or
similar.
Bright Ideas are usually ideas which either:
Makes your life easier.
Makes your life funnier.
Solves all or most of your problems.
Gets you out of the monster cave where you and your fellow travelers has been stuck for some time. This usualy happens right before the monsters return to eat you all alive, as some say; "right in the nic of time". (P.S. This usualy don't happen in our reality.)
See also: bad ideas