This is when Friday the 13th collides with Valentines Day. The next "13 Valentines" is in 2009, and it happens about a dozen times per century. But it's also considered the only Friday the 13th, to actually be good, for falling in love.
It's said that good over powers evil when 13 Valentines occurs; when bad boys and girls are able to actually fall in love.
If you combine the two names, Friday the 13th and Valentines day, the natural phrase that has come from this is 13 Valentines.