Usually, I've called it a cap. You've probably never thought much about it, or if you have, you've probably ignored it as a random design feature that regulates air pressure or prevents ink from drying out. And yes, having a hole allows you to close the lid properly without air pressure problems. But it also has another simple but ingenious purpose: to reduce the risk of deaths from asphyxiation.
Other pen manufacturers have followed suit and have also added larger holes in the top of their pens, he added.