- grown up, being adult.
- for adults only, as in "intended for a mature audience'
- for porn sites, mature refers to any woman (or man) over the age of about 40 or so.
Mature is a general catch all for pretty much anyone from a MILF to a granny. The mature market has slid down in age a bit at times because of the inclusion of the MILFs, who are often under 30 years of age. Mature women are sometimes refered to as a cougar.