A more thorough explanation:

Presenteeism is when employees come to work even though they are sick. This can make them less productive and spread their illness to others in the workplace. It costs U.S. employers over $150 billion every year.

There are a few reasons why presenteeism happens. Sometimes, companies make it hard for employees to take sick leave, so they feel like they have to come to work even when they're not feeling well. Other times, employees might not have good health insurance or any health insurance at all. This means they can't afford to go to the doctor and get better, so they stay sick and keep coming to work.

For example, imagine that you work at a restaurant and you start feeling really sick. You have a fever and a cough, but you know that if you don't come to work, you won't get paid. So you go to work anyway, even though you're not feeling well. While you're there, you're not as productive as usual because you're feeling so sick. You might also spread your illness to your coworkers or customers, which could make them sick too.