In a solution, one thing has dissolved another thing

In a solution, one thing has dissolved another thing. An example of this is salt water, where the salt has gone from a chunky solid to being completely dissociated in water. Another word for a solution is a homogeneous mixture.

Colloids, on the other hand, aren't homogeneous. Instead of having a dissolved by a solute, colloids have tiny particles of one thing floating around in the other. These particles are small enough that they don't settle to the bottom, but are definitely distinct from the thing they're floating in.