SMW attributes:

• has type::String
• allows value::M,F

Property: foaf:gender
gender - The gender of this Agent (typically but not necessarily 'male' or 'female').
Status: 	testing
Domain: 	foaf:Agent
Range: 	http://www.w3.org/2000/01/rdf-schema#Literal

The foaf:gender property relates a foaf:Agent (typically a foaf:Person) to a string representing its gender. 
In most cases the value will be the string 'female' or 'male' (in lowercase without surrounding quotes or spaces). 
Like all FOAF properties, there is in general no requirement to use foaf:gender in any particular document or description.
Values other than 'male' and 'female' may be used, but are not enumerated here. The foaf:gender mechanism is not intended to capture the full variety of biological, social and sexual concepts associated with the word 'gender'.

Anything that has a foaf:gender property will be some kind of foaf:Agent. However there are kinds of foaf:Agent to which the concept of gender isn't applicable (eg. a foaf:Group).