Box breath is also known as square breathing. This is because there are 4 steps to the technique and each step lasts for the count of 4.
How to use this technique:
Sit comfortably with a straight back
Inhale as you count slowly to four in your head, filling the lungs completely
Hold the breath while counting slowly to four
Exhale and release the breath slowly to the count of four
Hold the breath out for the count of four
Repeat the cycle five to ten times