Pimping in France is similar to in the U.S. when you make money from prostitution.
In France prostitution of course is legal as are brothels etc.
The "aggravated" charge alleges involvement in the habitual operation of a prostitution racket. Specifically, "aggravated' means on a regular and involved basis, and "pimping" means actually facilitating a prostitution operation, not just being a customer which is of course legal.
Prostitution isn't illegal in France, but making money off of someone else's prostitution is. Last December, DSK's lawyer Henri Leclerc admitted that his client attended sex parties, but he claimed that he was not aware the women there were prostitutes. If the latest charges against Strauss-Kahn are true, he was more than a mere attendee.