An action camera or action-cam is a digital camera that's been designed for filming action of some kind. Whatever sport or action you're into from Diving to swimming to skiing there's an action cam for you!
Action Cameras are designed to film the experience in a truly immersive way and as a result are often small, tough and lightweight, with some being dustproof, waterproof and Impact-proof as well! They're often available with a range of mounts and accessories for different types of use so you can find the perfect one for your action.
Action cams are almost the opposite of regular video cameras, they're small, inexpensive, simple to operate and tough.
You should have a think about where you want to mount it and what you want to get from it before making a decision. Are you more focused on the quality of the video? How well it'll survive in extreme temperatures Or are you just looking for something basic to take footage of your weekend escapades? The answers to theses questions should give you an idea of what features to look out for.