Stupid question first, I've seen it in a ton of posts.....What is natty PB? I know it's peanutbutter but what is natty?

The other question, in your opinion what the best meal replacement out there? I'm looking for one I can take at work between lunch and going home. Gotta be something really easy I can just mix up with milk since I don't have a blender or any fancy stuff at work.