What qualifies as a bear bag? I'm going on my first backpacking trip on the Appalachian Trail I can't find a bear bag. I see bear canisters but they're far too bulky I saw some other backpackers that seemed to use water resistant bags

We decided to use the bags for our days trips, and the safer canister for camping.  Canisters are bulky, but double as a stool. 

Here's a site for general info that is mainly about canisters.

http://www.rei.com/learn/expert-advice/bear-resistant-canisters.html

This one focuses on the effectiveness of various bags.

http://briangreen.net/2012/12/a-real-test-for-odor-proof-bags.html

On Google, you can search "odor proof bear bags" and click the shopping tab.