It's what comes up when you Google his name, a sexual definition created by Dan Savage to protest Santorum's unfriendly views on gay rights.
When most people Google themselves, they just grimace and move on (let's face it, Google rarely flatters any of us). But Santorum actually tried to get the company to change its search algorithm so that the sexually charged meaning of his name doesn't come up.
Sorry, Rick... I can't get Google to do what I want, either.