As ever with PPRuNe, there is a previous thread on the subject, in this case debating the (various) meanings of "complex single", both in the previous generally-accepted sense of "variable-pitch prop, retractable gear, etc" (still a valid distinction in the CPL training/testing world) and with reference to EASA's somewhat unhelpful hijacking of the term to mean something completely different
:
Complex Non-High Performance
From that thread:
Cobalt is not making it up. This is the meaning of "complex motor-powered aircraft" as defined by EASA in Basic Regulation 3(j).
It is unfortunate that they chose the word complex as it creates confusion with the common understanding of VP+RG+flaps. However it is important to understand the new definition as it has implications on Ptf, maintenance requirements, etc.