See how much skin is shown, and how much is not shown.
Basically, tropes that have one purpose: how much skin can clothing show before it's considered indecent.
Of course the amount will vary among cultures
, yet any degree is still often a way of Getting Crap Past the Radar
, which is one of the main reasons these tropes are so often used.
And since since a lot of people find partial nudity more sexy than full nudity
, this also makes many of these tropes fanservice
, as well as mildly Not Safe for Work