What is a Pagelet?

I've seen this term used quite a bit lately, in particular in conjunction with sites like FaceBook开发者_运维知识库 that load different areas of the page concurrently, calling the different areas of the page 'pagelets'. Is this actually a construct, a specific HTML tag, etc., or just a word to signify a logical area of a webpage that has no specific technical implementation?

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The term "Pagelet" is used by a number of product vendors to signify some kind of markup (generally HTML) than can be injected into web pages, and managed as an independent component. Hava a look at http://encyclopedia2.thefreedictionary.com/pagelet for a definition.

Pretty much any external web app or page fragment hosted external to the "containing" page could be called a pagelet - e.g weather "widgets", google maps etc. Some product (e.g. Oracle WebCenter Pagelet Producer) include a proxy server that allows pagelets to be created by clipping external apps, and also provide single-sign on, credential mapping, parameter passing and various types of filtering.