Everyday examples include beans getting stuck in a hopper in a whole food shop, or milk powder getting jammed in an upside-down bottle.
The term was coined by physicist Michael Cates, who asserts that such circumstances warrant a new class of materials.
The jamming thus described can be unjammed by mechanical means, such as tapping or shaking the container, or poking it with a stick.
Slight tilting or vibration is enough to enable the grains to shift, collapsing the pile.
Shaving foam is jammed because the bubbles are tightly packed together under the isotropic stress imposed by atmospheric pressure.