"Maiden name" generally means the surname a woman had at birth or adoption.
Geni.com appears to use it for men as well.
In some countries, women tend to retain their maiden names after marriage. In some parts of the world, that requires an active choice. A recent posting to a mailing list from Stephen Rowe (Melbourne, Australia; http://www.ser.id.au, http://www.mtbimages.com.au), pointed a warning with these links:
This page is a "stub" and could be improved by additions and other edits.