A semisolid is something that's not quite liquid and not quite solid, but somewhere in between. Think of peanut butter, toothpaste, or gel: they don't pour like water, but they're not hard like ice either. When you squeeze toothpaste from the tube, it holds its shape but can still be molded and spread.

Scientists use this word to describe materials that have properties of both solids and liquids. Jell-O wobbles and jiggles but keeps its form on a plate. Clay can be shaped and molded but doesn't flow away like water would.

These materials are thick enough that they don't just run away like water, but soft enough to change shape when you apply pressure. If you've ever watched someone scoop cookie dough or spread frosting on a cake, you've seen semisolids in action: they're thick and substantial but still movable and shapeable.