A net-girl is 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 worlds of Finnea Prime.
The Idanian operative "Arissa" became a net-girl on Finnea when she infiltrated the Orion Syndicate. (DS9: "A Simple Investigation")
- It's unclear if the buyer must also possess a dataport, though this seems a reasonable supposition. Also, no further detail is given on what precisely a net-girl is doing while sharing her mind with men. However, that's perhaps best left to the imagination.