If you have spent any time in Second Life, one of the first things that you will notice is that the avatars walk funny. Many people describe it as a “duck walk”. It looks awkward and silly and most importantly it doesn’t look like someone walking.
One of the first things that people often want to do once they join Second Life is get a decent walk (right after getting a nice skin and a fabulous flexi-prim hair). One way you can replace your duck walk is by finding some boots with a walk replacer built in. This is a fine solution if all you want to do is replace your walk, but if you want to replace your other default animations like sitting, standing, flying and jumping, you will want to use an Animation Override.
An Animation Override (or AO) is a scripted object that you wear. You load it with animations and it uses those animations to replace your default ones automatically. So when you walk, sit or stand, it plays the animations you choose.