MVVM (Model View ViewModel) is an architectural pattern based on MVC and MVP, which attempts to more clearly separate the development of user-interfaces (UI) from that of the business logic and behaviour in an application. To this end, many implementations of this pattern make use of declarative data bindings to allow a separation of work on Views from other layers.
Link: Understanding MVVM – A Guide For JavaScript Developers via Addy Osmani
An excellent overview by the always excellent Addy Osmani on KnockoutJS.
