What is the Master List?

The Master List is your complete inventory of everything you need to do. Every task, every commitment, every "I must get around to that" — if it matters, it belongs on the Master List.
Think of it as your external brain. The goal is to get everything out of your head and into one trusted place, so your mind is free to focus rather than remember.
The Master List is not your to-do list for today. It is the pool from which your Today List is drawn. You review it, you prioritise from it, but you don't work from it directly. That distinction is important — a long Master List is healthy and normal. It simply means you're capturing everything as you should be.