ALE is Ajax Linking and Embedding. In the same way that OLE (Object Linking and Embedding) allows Windows applications to embed each other's content, ALE allows Ajax-based applications to embed and enable editing content from other applications.
Google has done some similar work in v2 of their maps API. I wonder how Microsoft plans to to handle embedding in Atlas? The ability to encapsulate functionality into controls in the ASP.NET environment would lend itself well to this.