PI = principal investigator, or the leader of the lab. Also known as the professor. The closest comparison to regular jobs would be that the PI is the manager. They typically no longer do actual lab work and typically fulfill a role that is entirely managerial, so they’re often removed from and therefore entirely oblivious to goings-on of the lab. It’s a somewhat common occurrence for lab members to have a concern that the PI dismisses because they’re unaware of the severity of the concern, or for the PI to have a concern that lab members have already addressed