Is anybody acquainted with this term? Aren't able to find much about this around the interwebs.

It's cited within the CouchOne announcement. http://www.couchone.com/merger-technical-vision

Also known to here http://public.dhe.ibm.com/partnerworld/pub/pdf/courses/z1a06.pdf

I had been interested in that as well after reading through the question and so i requested their technical support. This is exactly what they stated:

If you're acquainted with CouchDB's _changes feed, and _update, _show and _list functions, that's the fundamental idea, to use that programming model to a lot of database internals.

I believe what it really means would be that the trigger could be fired on several "occasions", e.g. on update , on place, on remove etc..

My 2 cents