Muscle tone is very different from strength. The natural tension that our muscles hold while conscious is muscle tone. This can be maintained with regular activity and it is different from person to person and changes as we age. Even more technically, it is the natural resistance a muscle has to being stretched while conscious. This is very important to things like posture and balance.
Now if you meant the appearance of muscularity from exercise, there are two popular views of this. One is the pump from a hard work out where the muscles are slightly inflamed and full of water. The other is the overall muscle definition that is increased with regular exercise and overall leanness of the body. The “pump” diminishes quite quickly after a workout. Muscle definition will depend on the individual and their propensity to being lean, especially subcutaneously (under the skin).