Variation means a deviation from the norm, like the variation of colors in nature.
A variation from an accepted standard can be very important. For example, a variation in a heartbeat pattern can tell a doctor that a heart attack might be imminent. The variation in weather temperatures from what is expected indicates that our climate is changing due to global warming. But not all variation is a bad thing. For example, even within breeds, there is a wide variation in the coloration of dogs, a trait that makes each puppy uniquely lovable.