To send pictures back and forth removing a layer of clothing in every picture.
Like porn a sex picture is two people at it in a picture. Also why are you looking this up?.
What does sex mean? sex is defined by the lexicographers at Oxford Dictionaries as (chiefly with reference to people) sexual activity, including specifically.
Picture of Extreme closeup on sex word in dictionary stock photo, images and stock photography. Image 4091509.