It is an "Alert" or "Alert Recall" where all serving military are called back to their place of employment and prepare to deploy to places to be named in Orders. It can be on a small scale such as an Unit or Sub-Unit Level, a Bde Level, an Area Level, or right up to a National Level. Those called in by phone, radio, television, or knock on the door, will report immediately to their place of employment with all of their kit and prepare to move out. In the case of an Alert Recall, they prepare to move, but stay in their place of employment.
If on Exercise or Deployment, when someone says to "Bug Out!" it means to drop what you are doing, grab your kit and move out of that location, to another predetermined location. This would usually be a "Crash Harbour!" and is very paniced and quick.
Speed is of the essence.