Hygiene theater is when people do things to fight germs that don't actually make a big difference in keeping them safe. It's a bit like pretending to clean your room by just moving your toys from one place to another instead of actually putting them away properly.
For example, some people might constantly wipe down surfaces with disinfectant wipes, even if they're not really dirty, thinking it will keep them from getting sick. But the truth is that most germs are spread through the air or by touching things that someone with germs has touched, rather than from surfaces that aren't visibly dirty.
Similarly, some businesses might make a big show of constantly cleaning and disinfecting, even if the risk of transmission is low in their particular setting.
This isn't to say that basic hygiene practices aren't important - it's always a good idea to wash your hands regularly, cover your mouth when you cough, and stay home if you're feeling sick. But sometimes, people can go overboard with extra cleaning and other measures that don't actually do much to reduce the risk of getting sick.