The term woodshedding in jazz means more than just practicing. It is a recognition of the need to sequester oneself and dig into the hard mechanics of the music before you can come back and play with a group in public. There's something philosophical, almost religious, about the term. The musical treasures of jazz are not easily accessed. You have to dig deep into yourself, discipline yourself, become focused on the music and your instrument, before you can unlock the treasure chest.
At the same time, woodshedding is a process of demystifying the music. The amazing solo, the intricate bebop melody, the complex rhythmic pattern, can be learned, if one is patient. It is a humbling but necessary chore, like chopping wood before you can start the fire. The term woodshedding, like the term "axe" (slang for your musical instrument), evokes images of rural, rootsy beginnings. It is a reminder, conscious or not, of the deep roots jazz has in the blues, gospel, and the merging of African and European musical traditions under slavery.
Woodshedding is an outgrowth of the aural tradition in jazz, where a player works out by ear and intuition the music he or she heard played in public. While many jazz musicians have also been trained in written music, jazz improvisation developed aurally and orally, as older musicians passed on their innovations and discoveries to the younger, both through live performances and jam sessions and then, later, through recordings. The common theme between jazz and other musical woodshedding is the emphasis on the aural discovery of the right sounds, a trial-and-error process that hones your musicianship.
There is a lot of folklore and legend associated with woodshedding. Bebop legend Charlie Parker, after his embarrassing attempts to solo at several Kansas City jam sessions, spent the entire summer of 1937 honing his technique while playing a resort gig in the Ozarks. He took all of Count Basie's records, from which he learned all the Lester Young saxophone solos. At the end of this marathon woodshedding session, he reemerged as a mature player to be reckoned with.
John Coltrane and Eric Dolphy, both modern jazz innovators and saxophone legends, were renowned for their dedication to practicing and investigating new musical ideas. They would practice all day, and then practice between sets at their gigs, when the other musicians were hitting the bar and hitting on women. Coltrane in particular served as an example of the spiritual discipline that can be part of woodshedding.
Now that jazz is taught in universities and high schools, aspiring musicians have a multitude of resources for learning the art. There are a plethora of books, videos, even computer software for learning jazz improvisation. Woodshedding in the 21st century has taken on new forms. Still, the idea of woodshedding has not changed. Any musician who wants to be part of the jazz tradition has to pay his or her dues. You still have to take your axe in hand, go to the woodshed, and chop that wood before you can light the fire.