Thin privilege is having non-emergency and non-weight-loss surgeries covered by the UK government. For a specific example, for me to get my transition surgeries done, I would have to somehow get a BMI under 30 and waist measurement under 37in, since I’m definitely not that thin. Even though there’s not any widely-available conclusive proof that being fat on its own will increase the risk of complications, plus my physical health is actually quite good anyway.