Since it is made of gelatin and water, Jell-O is a solid that is suspended in a liquid. This happens when the solution cools after being heated and the proteins rebind, creating a matrix that traps the water molecules. A colloid is something like Jell-O.
Colloids form when one substance is equally and tiny spread across another. The other two forms of mixes are solutions and suspensions; colloids are one of these three. A colloid has particles of a diameter between 1 and 1,000 nanometers. The solid elements of the colloid do not sink to the bottom because of the uniform distribution of particles.