What is the difference between a colloid and a suspension?
A colloid is a suspension, but a specific type.
A colloid is a suspension, but specifically colloids have a dispersed phase where the mean particle size is between 1 and 1000 nm, and also they are sufficiently stable that they do not separate upon standing to any observable extent.
A regular (non-colloidal) suspension, on the other hand, may contain larger mean particle size dispersed phase, and can gradually separate on standing. A typical example would be something like a mixture of soil and water - initially it resembles a dark brown liquid, but after standing for an hour or so you end up with essentially a layer of brown solid, with a transparent layer of (predominantly) water on top.
A classic example of a colloid is something like milk. It is a suspension of oil droplets in water, but on standing it does not separate into two layers; adsorbed protein molecules give extra stabilisation to the suspension.