What are multi experience Fast Passes and how do you get them?

[egritz]

Did the ride go down at all during the FP window? That would be interesting if it didn't and they got the ME anyway.

Sorry, just seeing this question. I don't believe the ride went down at all....My husband said about 5 minutes after he left the line with our son he saw the notification on the app that their FP's had converted to ME passes.