“Critical” is a widely used term in Quality by Design, relating to anything which affects the safety or efficacy of the finished product. Dr. Brian Carlin at FMC BioPolymer explains why Critical Process parameters and Critical Material Attributes must be controlled to ensure the finished product Critical Quality Attributes necessary for safety and efficacy, as prospectively summarized in the Quality Target Product Profile.
https://international-pharma.com/wp-content/uploads/2014/01/Critical.pdf