Setu can mean a causeway, dam, or bridge, when combined with bandha it means the forming of a bridge. This is an advanced posture—you should not try it alone but with a teacher you trust. Other than upward facing dog, this is the only backbending posture in primary series.
This pose strengthens the back muscles and neck, correcting neck alignments. The throat is opened, stretching and cleansing the esophagus and the chest expanded increasing the capacity of the lungs. Due to the stimulation of our third chakra our digestive fire is increased by this asana.
This is the end of Primary Series! Whoo-hoo! You are now ready to begin the closing series.