A net-girl is a woman who sells access to her mind for money via the use of a permanently-implanted dataport. The practice is akin to prostitution, but there is no physical contact between the buyer and seller. Net-girls are known to exist on the non-Federation world of Finnea Prime.
The Idanian operative "Arissa" became a net-girl on Finnea when she infiltrated the Orion Syndicate. (DS9: "A Simple Investigation")