I know for me, it's having everything in the house in its place at all times; when I walk around, I'm constantly looking for things out of place.
Some have other words for this, but in my view, it's one of my obsessions.
Hmm....my current obsession is getting home maintenance done. For instance, we had the shutters repaired (cost a fortune) and I'm waiting for the electrician to get back to me to put up 2 ceiling fans, and then I'm going to be painting 3 of the upstairs bedrooms and the master bathroom this year. So I'm doing a lot of home planning and right now most if it is in my head.
My daughter doesn't live with us, but we still have a "bedroom" for her and her things. I want to make it more of a guest room and move a lot of her bins into the basement. She doesn't care about those things anymore anyway. Amazon goofed yesterday and put up an accent chair for $11 and I think it was supposed to be $111 so I bought it and it should get shipped by March if they don't cancel the order LOL Hey, I tried.
I've been more into forums lately than I was a little while ago. I was inactive more often on forums when I went kind of through a withdrawal from them, but now I'm on them nearly every minute of the day.
For me, it's definitely everything being clean. I have noticed over the last few years that I seem to hate it more and more now if things are not in place, if things are a mess, or if things are out of routine. Because of that, I have noticed that when things seem a mess or out of place or routine I get stressed quite easily.