When you go into the Ideate phase, you will come up with multiple ideas to solve the problem you have just investigated. How will je judge your ideas on the fit to your problem? You translate your findings in the Define phase into Design Criteria and you use these Design Criteria to "measure" the fit of your ideas to your problem.

First you list al your Design Criteria and explain why they are important (reasoning) then you prioritise your criteria so you can use them to validate your ideas.  

Your design criteria should be based on the research that you have done, so its a good idea to base the criteria on the validation board and the value proposition canvas. For example (you can use other methods to list your design criteria):

(c) ndw 2017