I'm not sure what the official name is, but by "summary fields", I mean for example "Open Notes" on a Shot. It's really the summary(count) of a query on linked notes with the status of "open".
We use notes to track various different things: client feedback, dailies feedback, render problems, asset problems, etc..
With the ability to create our own summary fields on cards, we could display counts of these different types of notes separately.
