Crosspicking is a technique often heard in Bluegrass. A lot of people think of it as doing banjo rolls on the guitar.
In crosspicking, the flatpick is used to pick a group of strings in a repeating pattern. The father of crosspicking is George Shuffler, who got the idea for playing this way when playing with Jim and Jesse McReynolds in the early 1950's. Jesse McReynolds was doing a similar style of picking on the mandolin. Later, Shuffler joined the Stanley Brothers band, where he used his cross-picking style extensively.
Most guitarists use crosspicking as way to accentuate specific passages in a song rather than as a technique applied to the entire song. It is a technique that can add richness and variety to a song when used judiciously, but can become monotonous and repetitive if used too much.
Crosspicking is a challenging style to play, particularly at higher speeds. Nonetheless, it is a valuable and rewarding technique to learn. You can see a short tutorial on crosspicking in our Study Tune section that shows how this technique can be used.