The David Allen Company: "GTD is the popular shorthand for Getting Things Done, the groundbreaking work-life management system and book by David Allen that transforms personal overwhelm and overload into an integrated system of stress-free productivity."
The important stuff is right there:
Capturing anything and everything that has your attention
Defining actionable things discretely into outcomes and concrete next steps
Organizing reminders and information in the most streamlined way, in appropriate categories, based on how and when you need to access them
Keeping current and ?on your game? with appropriately frequent reviews of the six horizons of your commitments (purpose, vision, goals, areas of focus, projects, and actions)