The correct definition for it is; it's the average wage of all people in full-time employment divided by gender.    It doesn't look at things like women working fewer hours than men and professions each of the genders choose.

As an example (according to the AMA), the highest paid medical profession is surgery, with the single highest paid profession being a brain surgeon.  Women make up only 19% of surgeons and 4% of brain surgeons.  Similar figures in the UK.

Conversely, women dominate the lowest paid medical professions such as pediatrician and gynocologist.

According to 1985 figures (latest I could find), only 2% of people in the mining industry are women and less than 1% of them was actually involved in mining.    Obviously, this means that women in the mining industry make a lot less than men if you do a genieric piss take of a survey on wages.

Not being paid equally for the same thing is highly illegal in the UK, yet under 13 years of Labour rule there were only 16 prosecutions for this.  That screams volumes about how realistic the problem actually is.  The way vaginalists and their cucks tell it, we should have had trillions of prosecutions a day for it.

I consider myself to be an "average" person.  I was in upper management at a government agency that oversaw a predominately male industry (oilfield).  So there are arguable reasons why the regulatory agency would have discrepancies of that sort, I honestly don't think them particularly valid.  YMMV.