A stairlift is a device for helping people getting up and down stairs who are not able to walk. For big stairs this means a rail which is mounted to the threads of the stairs. On this rail there would be a platform where you can place your wheelchair and move up the stair sitting in your wheelchair. For smaller stairs it is usually bot possible to mount rails directly to the threads. A design of stair lifts often used in this case is the rail connected to the site of the stairs or the wall. On to this rail we connect a chair and a motor. Usually you can not get your wheelchair onto this type of stair lift, you would need to get out of your wheelchair and sit down in this chair.
There are other names you might see used to describe this type of equipment like chair lifts and stair gliders. These are the same thing, and should not be confused by the chair lifts used by skiers. The first stair lifts were produced in the US in the 1930s. These were produced by the Inclinator Company of America mostly to polio victims. Today stair lifts are used both by disabled people, elderly people and people in general who have problems walking in stairs.