A suspension is a heterogeneous mixture in which solute-like particles settle out of a solvent-like phase sometime after their introduction. We use the terms 'solute-like' and 'solvent-like' because we are dealing with a heterogeneous mixture, while the terms solute and solvent refer to homogeneous solutions.
We apply the word 'suspension' when particles are big enough to eventually settle. If the particles are too small to ever settle, they are said to form a colloid.
Examples of Suspensions
Sometimes, in the right light, you will be able to see particles of dust floating in a room. Eventually the dust will settle on the floor and on furniture, and the room will need to be cleaned. Dust in air is a suspension.
If you go to a beach and mix sand and water in a bucket you will form a suspension. Given time, the sand will settle on the bottom of the bucket to leave clear water.