To the end-user in SharePoint, the content structure is built up by Site Collections and Sites. A site collection, from the name, is a collection of sites, including one top-level site, and any number of sub-sites below.
See http://technet.microsoft.com/en-us/library/cc262410.aspx for more information on site collections and sites.
In most cases knowing this bit of information keeps you afloat, but it doesn’t take long before you try to do something not documented on office.microsoft.com, and you start seeing the word web used every now and then. You might know all of this already, but for reference to the unknowing here are the relationships:
|Office.com documentation||MSDN documentation|
Being a developer I’m used to this and can quickly jump between the red and blue pill worlds, knowing when a Site means a site collection and when it means a single site (web).
And this is where the worlds collide this time in terms of Query Rules.