That word is in use, but not very common nowadays, and the meaning is heavily dependant on the context.
Examples could be:
- polite/honorific, although a bit antiquated: "Was wünschen Madame zu speisen?"
- ironic/derisive, to a girl/teenager: "Wenn ich Madame noch einmal dabei erwische, wie sie an meine Kreditkarte geht, setzt es was!"
- Mainly used to put said girl's head straight when she thinks she's entitled to something she actually isn't.
- Warning: The english word "madam" is sometimes used to denote a female procuress, too, and this connotation did make some headway into the usage of this word in German.
Anyway, "gnädige Frau" is a more up to date replacement for "Madame", especially for the more positive connotations.