A skeuomorphic UI element where a wheel can be spun to change a displayed value.
Spinners are UI elements that fill the role of a dropdown list.
On some systems, they look like wheels or rolls, which can be spun (usually vertically about a horizontal "axis"), to display a set of values. They are often used for to cyclical sets of values, and as such are typically found as part of date or time pickers.
On Android, a spinner is used as a view control and is an space saving alternative to tabs.