See also: Skinning Tutorial.
Skinning is one of the fundamentals of all osu! game modes. It enables users to derive from the original skinning elements to create their own!
Over the years of osu!, skinning has changed dramatically in style. There are various ways that you can skin osu!
Skins vary from for-fun to a central theme (e.g. anime or group of people) to those that are nigh impossible to play with (e.g. oversized hitbursts, invisible followpoints). Another type of skin are pro skins, where they maximize play field visibility and minimize visual obtrusions (e.g. replacing hitbursts with blank images).
See also: Ranking Criteria/Skin Set List.
If your skin contains a single element from the listed sets in the Ranking Criteria, it must contain all of the other elements in said skinning set.