A placement is a trick where you place one of the objects you're juggling onto some part of your body where it will remain stable until you take it back off, for example putting a ring around your neck.
If you're juggling more than three objects to begin with, you can switch to the pattern for next lower number of objects while the one object is out of the pattern, or you can keep throwing like you would if you were still juggling all the objects, and then grab the object and put it back into the pattern when you have a free hand a few throws later.(video)