You might have heard people talking about 'mashups' lately as companies like Google,Yahoo! and Facebook look for new ways to innovate their provision of content between applications.
A Mashup is basically a website or web application that seamlessly combines content from more than one source into an integrated experience.Content used in mashups is typically sourced from a third party via a public interface or API. Other methods of sourcing content for mashups include Web feeds (e.g. RSS or Atom). (Wikipedia)
It's basically sites sourcing content from other sites so that they don't have to provide all the content themselves and they can present more value to the user.
Unlike the days of old when companies like PlayStation used to protect their application programming interfaces to ensure that only selected game developers could develop for the platform, the new players setting the field are looking for smarter and more cost effective ways of providing value. If the 90s Internet was all about community, then we thought that content was king, the future is most certainly about collaboration.
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Google does the mashup dance