(1) In object-oriented programming, a programming unit that groups together a data structure (fields) and the operations (methods) that can use or affect that data. Objects are the principal building blocks of object-oriented programs. (2) In Mach, a collection of data, with permissions and ownership. (3) In AppleScript, an instantiation of a class definition, which can include properties and actions. (4) A group of bright, high-intensity pixels in an image, as opposed to the darker pixels, which are considered part of the background.