If a web page uses the jQuery library it usually makes sense to link to copy hosted on an external content delivery network (CDN). You don't have to keep an updated copy on your site, the client may already have this copy cached, and the CDN has high bandwidth connections. Google, Microsoft and jQuery themselves offer CDN hosted jQuery.
I use the Google version and call it with this line:
That is fine, but what happens when a new version comes out?
In these cases some sites will offer a 'latest' url that automatically points to the most recent version.
Google does not do that - but they offer something similar, and which might be slightly better.
If I want version 1.7.0 and nothing else then I use the link given above.
If I want the latest version in the 1.7 series then I use:
And if I want the latest version in the 1 series then I use:
Note that you don't always want to use the most general form. New releases are not necessarily back compatible. But you have the choice.