There is a post related to the #NoEstimates discussion titled, Introducing Deliberate Discovery. It's one of those interesting topics that doesn't use the same words across most domains.
The word Plan in our domain is a Strategy for the successful completion of a program. The Integrated Master Plan (IMP) says what steps need to be taken to increase the maturity of the deliverables over the life cycle of the project. Here's the elements of project success at a minimum. The IMP/IMS is one. But risk, packages of work, the delievrables, Measures of Performance, budget spreads for the work, and other lower level artifacts are used as well.