What does "+2 hours after event" mean?

That means once your event ends, you'll have up to two hours to retrieve your vehicle.

Some locations near venues set up "event-based time-frames" for event parking with default 1- or 2- hour timeframes before & after the event, during which you'll need to arrive and depart. Any amount of time "after the event" that your pass states will correlate directly with an actual defined end time for the pass. It's still important that you don't overstay the end time on your pass; while some locations are a little more forgiving of events running late, they're an exception to the standard.

For more info on violating the timeframe on your pass, refer to this article.