In this wiki we talk about “bridge instruction”, that is, “special” courses to pass from one aircraft category to another: for example, from a helicopter PPL to an airplane PPL, from an airplane CPL to a helicopter PPL, from a glider license to an airplane PPL.
Obviously, all within the scope of a European license because, if a person has a license that is not issued by EASA, he or she must request a conversion (which will be discussed in a chapter later).