Semantics is the systematic study of how people attribute meaning to objects and interact with them. User interface design focuses on inputs, or what a user does to an object, and outputs, or what the object produces in response. The iPod has intuitive inputs like pressing play and obvious outputs like playing music. Its clickwheel scrolling motion is also intuitive and distinct, making it well received. The iPod's digital mapping, or layout of menus and buttons, is designed so that most tasks can be completed in four steps or less, with everything having a clear purpose.