BigWigs is a boss encounter add-on. It consists of many individual encounter scripts, or boss modules; mini add-ons that are designed to trigger alert messages, timer bars, sounds, and so forth, for one specific raid encounter. These encounter scripts are activated when you target or mouse over a raid boss, or if any other BigWigs user in your raid does. In most cases only one module will be running at any given time.
If you're looking for boss encounter scripts for 5-man dungeons, these are not in Big Wigs, but live in their own add-on; LittleWigs.