When it comes to sex, hardcore stands for the - in the truest sense of the word - somewhat "harder" variant.
Should it be a typical opposite to well-behaved Flower sex it is definitely "hardcore". Here, deep feelings rarely play a role. Hardcore is much more about hitting the other person hard and often also hard. dirty to fuck.
It is therefore self-explanatory why hardcore is mainly used in porn. Hardc. Strips are known here for using, among other things, camera angles in which everything can actually be seen in detail. For comparison: in soft porn, the sex is often shown from a slightly greater distance and nowhere near as directly as in the hardcore variant.
Even though the term has become popular with regard to sex and films, translated into German "Hardcore" actually only means "belonging to the hard core". Thus, in a way, an extreme is described here. Other well-known terms on the subject are, for example, "Hardc. Fan" or "Hardcore athlete". They also stand for the fact that someone pursues their passion particularly intensively - just like in hardcore sex.
The definition of what exactly is "hardcore" should certainly be left up to each person. While for some people it is already extreme to get sprayed in the face in connection with a cum shot, for others hardcore only starts with urine games and co.
Especially when two gays meet via chat and arrange to meet in real life to have "hardcore" sex, these "little things" should definitely be clarified beforehand. Everyone has different limits here.