Some context: for example let's say I have 7 counties (a polygon file), a point dataset with points scattered all throughout those counties.
I've got a webmap with the above content, and now I'm building a web application that accesses that map. The goal is to have the one web map, accessed by 7 web applications (one customized per county with it's own layout, widgets, color scheme, etc...). What I would like to do is essentially have an active definition query on the point dataset to only show points that fall within the county specific to that web application.
A parallel to a desktop version of this task would be Page Definition on data driven pages, for example.
In short, we'll have 7 web apps, 1 web map, and I want to query the data (hidden from the user) at the Web App level.