There might be certain situation in which it is advised to not polish a certain surface. This can be due to damage, time limit, thin surface or other factors. Knowing when not to polish might be as important as knowing when to polish.
The minimum paint thickness is an indication that there is no paint left to polish and should be avoided as much as possible. The downside is that this thickness is difficult to monitor or measure. Going passed this minimum thickness will result in strike-through of burn-through.
Applicators are products that are used to spread, apply, rub or buff a certain product to a certain surface. These can also be referred to as an applicator pad. There are many several differen shapes, sizes and material that are used for this.
A finishing polish is often considered the last step in the polishing process. It is a very fine polish that has a low grade of cut but a high level of perfect finish. A finishing polish can remove oxidation, marring, very light swirls and some of the minor imperfections.
A medium polish is a polishing product with a certain level of cutting. It will not remove RDS or severe surface imperfections, but it will will remove swirls, oxidation and several others. It is the most common step after cutting/compounding and if followed up by a finishing polish.
Plexiglass/perspex is a very soft type of plastic (Polymethyl methacrylate) that is very rarely used. Just like glass or paintwork, it can suffer from surface imperfections. Swirls and scratches can be very visible because it is fully transparent.