Screenings are health checks for specific conditions and diseases. You attend screenings before you have any symptoms, as the aim is to identify a problem in its earliest stages when it's easier to prevent or treat. The NHS has multiple national screening programmes - if you take up screening when it's offered, you can stack the odds of a healthy older age in your favour.
This is a companion discussion topic for the original article at https://patient.info/news-and-features/health-screening-in-the-uk