David,

PMI is rather tight-lipped about the non-PMBOK sources used for the PMP exam. So in order to be 100% safe, you would need to read every single book about project management that has ever been written...

That much said: It is less important to memorize the definition of a specific term (PMBOK-based or from another source). It is more important to understand how this term/concept fits into the PMBOK way of managing projects in a real life scenario.

Thus... focus on understanding how terms/concepts are used rather than how they are described.

When I run across acronyms that are not discussed in the PMBOK (glossary), but seem relevant to the field and practice, should I be learning these for the exam? I know not to “memorize” them all, and that some may be pertinent and other not, but for example, ABC (below) seems like something to know.

David

Activity Based Costing (ABC)
It is important to note that in traditional costing the assumption is that products consume resources. ABC contrasts traditional costing by assuming that products consume activities and activities consume resources. Once the product or service activities are identified, costs are allocated to the product or service according to the amount incurred by those activities. This method of allocating costs provides a benefit for making decisions regarding different types of profitability and project accounting (Awasthi, 1994, pp 9-10).