A rollator is just a special type of disability walkers. Rollators are often called wheeled walkers, as that is what they are, walkers with wheels on all of their legs. Some walkers have wheels on only two of their legs, they are sometimes called wheeled walkers, but when we talk about rollators we mean walkers with wheels on all of their legs. It doesn’t have to be 4 wheels, some rollators have only 3 wheels. A 3 wheeled rollator is sometimes easier to push and move about inside, through crowds of people, in narrow hallways and such.
There are some rollators only aimed at indoor use. These rollators have smaller wheels than the outdoor ones. They are often also not as heavy and robust as the outdoor rollators are. Most types have some form of seat that you can sit down on if you need a break while walking. There is usually one break on either front wheel which you put on if you want to sit down on your rollator. The breaks are often also use to take small radius turns.
Rollators are just like regular walking frames often made of sturdy, anti-rust aluminium. Most of the models are rigid, but there are some models you can get that are foldable as well. The foldable rollators are usually lighter and easier to pack, but not as solid and safe as the rigid types.