MCTB is the abbreviation for the title of a book called Mastering the Core Teachings of the Buddha, an Unusually Hardcore Dharma Book by Daniel Ingram.
It serves as a conceptual and terminological foundation and reference for a significant portion of the discussions on the DhO, and so reading it can be of value to understand what people are writing about and debating.
A free version is also available on-line at Interactivebuddha.com and here in chapter/wiki form.
As of March, 2012, Daniel has begun to modify this version here to elaborate and expand on various points, so this version will begin to diverge from the original as it is worked on. It contains links to more wiki sections that expand on the original ideas and hopefully will make them more clear.
This work is the property of Daniel M. Ingram and all rights are reserved. Feel free to quote it so long as you do not quote it out of context or alter the quote.