AFAIK it could also be a pet in addition to UM, wheelchair or other assistance request, etc. This is the stuff that sends you to the special services counter at major DL airports. However, I'd be a bit surprised if special meals were included.

The last time I had SSSS I was unable to complete OLCI due to some sort of government regulation, or at least that's what my hotel concierge told me. It was an international flight to the USA.