Flyweight is a software design pattern. A Flyweight is an object that minimizes memory occupation by sharing as much data as possible with other similar objects; it is a way to use objects in large numbers when a simple representation would use an unacceptable amount of memory. Often some parts of the object state can be shared and it's common to put them in external data structures and pass them to the flyweight objects temporarily when they are used.
A classic example usage of the flyweight pattern are the data structures for graphical representation of characters in a word processor. It would be nice to have, for each character in a document, a glyph object containing its font outline, font metrics, and other formatting data, but it would amount to hundreds or thousands of bytes for each character. Instead, for every character there might be a reference to a flyweight glyph object shared by every instance of the same character in the document; only the position of each character (in the document and/or the page) would need to be stored externally.
Reference:
http://en.wikipedia.org/wiki/Flyweight_Pattern
