Sample table of definitions
The ability to reuse content via a shorthand reference. This is often used as a slang term (a verb, like "google" is used as a verb) for using a content reference (
The open toolkit is what processes your DITA files to transform them into webhelp, pdf, and other outputs.
There are other processors besides the OT that can achieve similar results.
OxygenXML does use the Open Toolkit to do its processing, but xMetaL uses another processor.