Test Design Definition

There are numerous variants out there what exactly "Test Design" means.
Having tried to explain the matter several times lead me to the following definition which I find even more solid than my definition of testing.
This is how I put it:

Test Designing is prioritizing of an infinite list of all the possible inputs by the risk of not knowing the actual output.

I like this definition because:

• it implements the agility of testing time-frames
• its corner stone is risk - the main/only reason of doing testing at all

 And by inputs I mean everything that is needed for testing: data, steps, environments etc. And outputs are the system-under-test's reactions to our testing.