(https://www.mindtools.com/media/Diagrams/allen-input-processing-diagram.jpg)
An input is something that you need to take action on. Allen defines it as, "anything you have allowed into your psychological or physical world that doesn't belong where it is, but for which you haven't determined the desired outcome and next action step."
These inputs can be anything from thoughts that you've had about a new project, to emails and documents that you've received, to an invoice that you need to pay.
The main benefit of the tool is that it helps you quickly take action on all of the inputs that come your way. This means that you can focus on your objectives, instead of worrying about something that you might have missed.
There are three main stages in using the technique:
Collecting.
Processing.
Reviewing (not shown on the diagram).
Let's look at each of these three stages in greater detail, and discuss how you can apply this process to manage your workflow...
https://www.mindtools.com/pages/article/allens-input-processing.htm