There is no difference. To abseil and to rappel are the same thing. Both are rock climbing terms.
Listed below are some rappelling (a.k.a. abseiling) devices that you can use.
The rope follows an “S” path around two bollards. True bobbins have the center of each bollard fixed to the frame. They come in plain and stop versions. False bobbins have bollards whose centers move with respect to the frame.
Rappels using carabiners only or carabiners and brake bars only.
Devices that look like an “8.” Deaf eights don’t have ears; obviously eights with ears do. There are complex eights with moving parts, and toy eights that are not intended for rappelling.
Fixed Multi-bar Devices
The rope snakes around at least three bollards, all of which are fixed.
An ill-defined catch-all category, but generally the rope wraps around a rod.
Another ill-defined “catch-all” category for devices with horns or prongs.
Poly-bollards or Fixed Multi-bar Device
Descriptive terminology for the rope that snakes around at least three bollards, at least one of which moves to provide a stop function.
Devices with frames that accept a number of brake bars, at least some of which can move on the frame. J-frame racks have an open side, U-frame racks do not.
Devices where the rope wraps around a drum. The drum axis can be horizontal or vertical.
Devices with an enclosed rope channel and a control lever.
And I will finish off with another video on the do’s and don’ts of rappelling:
I would suggest that Mike Barter’s video should not be taken in the place of hands-on training, but it is a reminder to those of you out there who know what you are doing, and it is a continuation of his shorter one on rappelling that I posted earlier.