ETA: indoor or outdoor -- it depends.
For me, they are "outdoor" as long as the weather allows. So, typically, in my climate, from late September up until mid to late December -- and then intermittently, (if lucky), between then and mid-March. At which time I start wearing them more regularly again until mid-May or so.
Since I work at home, I don't really wear "indoor" shoes very often in winter. Except for YLF photos, I tend to wear slippers inside. But if you wear shoes indoors then you could wear your booties inside.
And I confess, there were times last winter when I did, just to enjoy the feel of them on my feet in a year when I was sad that they could not get worn more outdoors!!
Note there are different kinds of booties, too. Some are more "shoe like" -- not simply in the way they are cut at the vamp ("shooties") but also in their level of refinement. Others are more rugged or boot-like.
Compare a refined Chelsea boot (which arguably counts as a kind of "bootie") with Blundstones, for instance.