The best summary I could find is on Wikipedia [0]. Summary: put stuff away that you aren't using and keep things you need together and within easy reach.
I would say it's a bit larger than that, at this point.
There's (of course) a sub-reddit for folks who like to watch others knoll.
One proponent is Adam Savage from Mythbusters [2], and often refers to the term (and knolls model sets, tools and so on) and I don't think it's being done in reference to Tom Sachs any more.
I feel a little grosser knowing that but this activity, of maintaining your space, I like so much. The term "de-cluttering" comes to mind but it's so obviously a chore, a cost, maintenance, a reactive price. Anything that sounds active, moving forward, sounds much better.
it is not explained, only youtube link, cannot access