Hey Biscuits,
The answer is in the subject line, but just in case you or someone reading this post later don't know what a Bug Out Bag is, it's a pre-packed bag or backpack or something with what you think you would need if you suddenly had to leave your home. You can build one for leaving the city and heading out into the wilds, and/or one for leaving your burning home & staying in a hotel for a few days, and/or one for evacuating your neighborhood and living in an emergency shelter or with a friend or relative. They can be as short as overnight, or as long term as all the camping gear you can carry. A big one might be designed for throwing in the trunk/boot of your car. A small one might be carried by hand like a small suitcase.
I suppose BOB could also mean Bug Out Box, a form of caching where you pack, seal and label a box, which you give to a friend to keep in a closet for you should you ever have to vacate your home and stay with them. Food, clothes and a sleeping bag would go a long way toward keeping you from being a burden on them. The pre-arranged agreement would also give you a specific place to head, rather than trying to figure out in the middle of a crisis who might agree to take you in on short notice. If you keep a few such boxes for friends and relatives, and give out such boxes for them to keep, you will have created quite a nice little network of "safe houses" for you and/or your loved ones, should you or they ever have to run and hide or just wait it out.