Under the Humphrey-Parkes nomenclature, the main adult plumage, especially when it is produced by a complete molt, is called basic plumage. In most birds, the non-breeding plumage, which is worn longer than the breeding plumage, is known as the basic plumage. In birds that molt only once a year, the regular and only plumage is known as basic plumage.
In some birds, a partial molt occurs before the bird breeds. This plumage is known as the alternative plumage and is generally what was previously known as a bird’s breeding plumage. If a bird produces a third plumage in addition to the basic and alternative, it is known as supplemental plumage. This plumage is most frequently found in ptarmigans. The unique plumage of a juvenile bird is known as juvenile plumage.
When the bird is molting, the molt is known as a prejuvenal, prebasic, prealternative, or presupplemental molt, depending on which type follows the molt.
For birds that do not completely molt into full adult plumage the first time, a numbering system is used to signify which plumage it is in. For example, for the first time a bird enters basic plumage, the plumage is known as first basic plumage; the second, second basic plumage. The numbers are dropped after a bird achieves its full adult plumage.