1.  A web proxy filter designed to block access to "offensive" websites; typically installed by parents trying to filter their chilren's access to the Internet, or corporations trying to do the same for their employees.   (Most NetNanny programs, whether they use a site blacklist or a "smut detector" algorithm, have a high degree of both false positives and false negatives).

2.  The brand name of a software package that does #1 above.