Well I reckon that if you had a pound of fat on a plate beside a pound of muscle, they would both weigh the same.
Ok, that was a bit cheeky. Muscle has a higher density than fat. If one pound (1lb) of muscle is setting next to one pound (1lb) of fat on the plate, the portion of fat is much larger even though both portions weight the same. Muscle is leaner. The more muscular you are, the tighter, firmer, and thinner you appear, even if you never lose a pound.