the propery of various gels of becoming fluid when disturbed (as by shaking)
Any substance that is cabable of being both solid and liquid at the same time.
When you are enjoyng some french fries and you want some tasty ketchup, you shake the bottle to get it to come out. The property that helps you here is thixotropy.
Ketchup is a remarkable substance. Thank you, Kurt Vonnegut, for pointing that tidbit out.