Historically, pocket doors were a common design element in houses. The pair of doors that slid right out of sight into pockets in the wall was a common feature of elegant homes in the 1890's. Over time, pocket doors fell out of favor, probably because they were hard to open and close, noisy, and often came off the track. Nowadays, however, pocket doors are making a comeback. They're still practical (you don't need to leave floor space just for a door to swing open), and newer pocket door designs are quiet, strong, easy to operate and seldom jump their tracks.