What is this so called "best sex"?

I have heard this term so many times and someone actually said this as a quality that they have (for marriage) but what exactly is "best sex" or is it a subjective thing?

I know it is a taboo topic but I am not a pervert, I just want to know this from the perspective of Muslims because we only get to have one marriage and we don't have any reference most of the time to compare it to.