This is a term from physics and engineering, so there are lots of very technical definitions (involving lots of math). I’m greatly simplifying here.
This is when an object experiences load against one part of it, that’s not applied against another part of it. For instance, if a wall is fixed at its base (as most all walls are) and the wind blows at the top of it, this is shear load – there’s a force applied to the top of the wall which is not applied at the bottom of the wall.
Related to this, shear is when two surfaces move across each other at different speeds. The architect Frank Duffy discussed shearing layers as a design principle where the different conceptual “layers” of a building move at different speeds – the land, the walls, the furniture, etc.
The concept is the same as in physics – if you take a clump of dirt in both hands, one on each side, and pull one hand back while pushing the other forward, the clump of dirt will be subject to shearing stress, and will pull apart, the two sides of it moving in different directions.
Also related to this is “wind shear.” This is when the wind is moving in opposite directions in a short distance. So “layers of wind” are “shearing across each other.” This is very dangerous for landing airplanes, as the external forces applied to the plane can change very suddenly as the plane descends.
Why I Looked It Up
I was touring a new residence hall which was under construction at my alma mater. There was some discussion about how the external walls were load-bearing, so there were no columns in the middle of the building. This required some extra support to reinforce again “the shearing load.”
I nodded like I understood. I did not understand.