It is a euphemism for " anal sex " in the sense presumably vaginal penetration as " 34 main route; and anal penetration as " alternative route ". The term was widely used in radio reports where it could not be very explicit because of the time protected for minors; and - if I remember correctly - it was coined by satirist Eduardo Javier " Cabito " Massa Alcantara.
* Only one "like" per meaning and day, the more "likes" the meaning will appear higher in the list
