Here is a shaft
Many weavers and teachers call it a harness. We should know they are one in the same, but that shaft is the more correct term.
The photo shows the shafts in a loom. They raise or lower the warp threads.
Here is a shed
It’s the space where the shuttle goes. If there were no shed one would have to physically go over and under the warp threads. This is one of the main jobs a loom does: make the sheds.
Here is a view of a shed in a loom.
This photo shows NO SHED. What it does show though is the shafts. None are raised or lowered.
The sheds often are created by pressing on treadles.
The sheds can be created by levers if there are no treadles on the loom.
For a loom to be a loom it must be able to make sheds. However, rigid heddles do not have shafts. Instead, they have a rigid heddle that creates the sheds.
The sheds are created by lifting and lowering the rigid heddle.