Web page saved by the Safari Web browser; contains HTML and images so the page can be loaded fully at a later time even if the computer is offline, or not connected to the Internet.
Safari Web archives can be viewed in Safari as well as the iCab and Cruz Web browsers; they may also be opened with Apple TextEdit, but the contents might not appear correctly.
Program(s) that open webarchive files
Mac: Apple Safari; iCab; Cruz; Apple TextEdit Windows: Apple Safari
Information from FileInfo.com - The File Extensions Resource.
http://www.fileinfo.com/extension/webarchive