What does it mean when a session is highlighted in red in the PgAdmin dashboard?

I've noticed sessions being highlighted in red recently though this never occurred in the past which leads me to believe it is a new feature. It appears to only occur on hanging queries. I looked through the PgAdmin documentation as well as change logs for all recent updates but could not find an explanation. Here is an example of how it appears:

The session is running a query (state active), but is blocked and has to wait.

Often that blocking event is a database lock, but in your case it is IO: DataFileRead, which means it is waiting for an I/O request to complete.

If you see a lot of active sessions in that state, that is a clear indication that your I/O system is overloaded.

StackExchange Database Administrators Q#300647, answer score: 10