What is the part of the backpack (for eg.) that's held to shorten or lengthen it? See detail for image.

There is the part of the backpack strap that’s held with one hand in order to pull the strap to either to shorten or lengthen it. What is that part called? Edited.
http://www.gearforlife.com.au/wp-content/uploads/2013/04/BST1.jpg
http://tinyurl.com/yyk8trtf (images of backpcks)
https://www.bottegaveneta.com/ca/backpack_cod45408560kp.html?tp=53036&gclid=EAIaIQobChMIu5yN74Di4AIVAw5pCh2CRQV9EAQYAyABEgIkRPD_BwE Edited to add.