wage gap what is it

Today in the house the term wage gap was used in a lot of the questions. Heidi needs to know ,are we calculating this number correctly.
Apparently the formula used goes something like this.
[divide the median earnings of full-time, year-round, working women by the median earnings of full-time, year-round, working men]
This method will only work if there are men only and women only occupations, in today’s world there are women bulldozer drivers and male nurses as well as male and female servers and pilots and cabin crew with men and women  getting equal pay  . In reality there isn’t a wage gap between men and women doing the same work in the western world.
What Heidi believes the issue should be is equal pay for equal work example ,should a person working as part of an airline cabin crew make the same as a restaurant server, or a day care person and a preschool teacher be paid the same.

Will some one out there help Heidi out with this , are we calculating a wage gap that is not there and should we be looking at wage equality a little closer.