Chum Kiu is the second primary form in Wing Chun training.  It literally translates as "Sinking Bridge".  As with the Siu Nim Tao (SNT) it is designed to train certain aspects of the Wing Chun system in a foundational way.  The Chum Kiu builds on the SNT by adding the mobility and dynamic movement required to perform Wing Chun from before and after bridge contact.  Sinking, turning, stepping, kicking and controlling your opponents bridge with the techniques learned (and mastered) in the first form.