Where I work, they fall under the heading of "chores", for which the usual definition given is "something that will improve future velocity". Engineering owns

Where I work, they fall under the heading of "chores", for which the usual definition given is "something that will improve future velocity". Engineering owns these and gets to prioritise them as necessary. It's usually done with an eye to the current backlog of stories and bugs that product has prioritised. Sometimes chores get done opportunistically. You have a time gap, you grab a short chore and do it. Or you might spin one out of a story as a kind of marker of known tech debt. Sometimes engineering sees a heavy piece of tech debt that is a millstone and just goes ahead with it. Usually this ties up a track of work that becomes unavailable for product work, sometimes for weeks.