confused how the author is defining 'application'. Is it a server-side or a client-side entity? Seems to use it interchangeably at different points in the text

confused how the author is defining 'application'. Is it a server-side or a client-side entity? Seems to use it interchangeably at different points in the text, perhaps purposefully, perhaps not. Or if there is another property that that defines it as an "Application", what is that? (and how is that different from a 'Resource')