When some dude pops a woody and someone else notices his rock hard yogurt cannon then said first party must identify the underlying cause of his unnaturally erect wang. This is the "erection direction".
Most people signify the erection direction, or ED, with a subtle finger. If you're feeling bold use your meat steak to point.
Woah...Isaac. You have a massive hard on right now. Wheres the ED?
Yeah the erection direction is right over there. *points at Mariah*