Sometimes a mutation occurs that alters the colour or pattern of a budgerigar's markings. If this is able to be passed on to chicks it can become a new variety. The variety is separate from a budgerigars base colour. It can occur on any colour and is basically overlaid, so you would describe your budgerigar by both its colour and its variety. For example a wild budgerigar would be a light green (the colour) normal (the variety), or you may have a skyblue (the colour) opaline (the variety).
Normal is the term for budgerigars whose markings match with the wild type. The budgerigar can be any of the basic body colors, but so long as it has the wild type markings it will be of the normal variety. So you can have skyblue normal, grey normal, dark green normal.... etc.
Here are the several different varieties with wing and markings that are not the wild type (normal).