A erection one would get in pre-historic times, such as cave (rock) men
"I poked my head into your window and betty was undressing. She saw me there, but she didnt stop."(Barney)
"What?"(Fred)
"She didnt stop. I mean, she saw me there looking at her, but she kept undressing."(Barney)
"Whoa are you serious?"(Fred)
"Yeah, i got an erocktion."(Barney)
An art form consisting of both erotica (in the form of porngraphy) blended with a form of rock 'n rollmusic, including all subgenres of rock, such as heavy metal, classic rock, southern rock, etc. Usually this art form shows people having some type of sexual relations to the tune of any type of rock, or the rock music can be part of the background and not actually part of the action.
Jenny and Becca were engaging in erocktica as they pleasured one another while in time with Lynyrd Skynyrd's "That Smell."
This is some pretty mediocre erocktica. The girls are hot, but they could've picked a lot better music than Air Supply.