Hammer Ons and Pull Offs are advanced techniques used in the Guitar Hero series of games. Many fans know these by their common abbreviations, HO's and PO's . Although labeled as advanced per se, it is relatively easy to learn how to perform the technique, but to master it is a totally different story. Indeed, in order to perform the insane solos that the game sends at you, HO's and PO's are not only recommended, they are essential.