Boolean field for EE2 that will, when set to true, set to false the same field for all the other entries in that channel. Good if you want a "featured entry" without needing to remember to unset others or depend on publish date as to which one is displayed on the site.
By default, true/false labels are Yes / No - you can set them to whatever you want in the field settings. The actual value stored is always 1 or 0.