I'm not OP and I could be wrong, but I believe they meant pronouns typically used by people who are some sort of "demi"-gender (i.e. demiboy, demigirl, demigender, etc.), which would usually be multiple sets of pronouns? For example, the assumption is that someone who is a demiboy would use he/they pronouns, someone who is a demigirl would use she/they pronouns, etc. However, it is more than just demigender people who use multiple sets of pronouns and demigender people are under no obligation to use any specific set of pronouns, so I could be wrong. I don't know if that's what OP meant, but my guess would be that that's what it is. Some examples of multiple sets of pronouns would be he/they, she/they, he/she, he/she/they, etc! The way they're used is you can either alternate them interchangeably at any point (Ex: "This is my friend [blank]. Did you know that they did this really cool thing all on his own?"), or you can alternate back and forth per each sentence (Ex: "This is my friend [blank]. Did you know they did this really cool thing all on their own? She's so awesome, isn't she?"). (You might already know some of that, but I thought I'd elaborate just in case.) I hope that helps!