The gov.UK website states an individual might apply for a work visa and get paid less if “you have a science, technology, engineering or maths (STEM) PhD level qualification that’s relevant to your job (if you have a relevant PhD level qualification in any other subject your salary must be at least £26,100) you have a postdoctoral position in science or higher education”

https://www.gov.uk/skilled-worker-visa/when-you-can-be-paid-less How exactly are they defining the difference between a post doctoral level qualification and actually having a PHD? Is there a difference? Or are they the same? Asking as a US student currently working toward a Material Science Certificate of Achievement as a career starter.