A "static hold" is a fitness term that means holding a position without any movement. It helps to strengthen muscles and improve stability. Full definition
This exercise consists of 3 static holds with each one targeting the biceps from a different angle. (unique-bodyweight-exercises.com)
You can make the exercise a lot more difficult by including static holds on each rep by holding the bottom, middle and top positions for 5 seconds. (unique-bodyweight-exercises.com)
Two ways that I make pull - ups more difficult is by changing the tempo to force them to go excessively slow as well as incorporating static holds at different points in the movement. (onnit.com)