"A Muggle-Repelling Charm can be used to prevent Muggles from seeing magical related places or items."
From the Story
Discovered in Book 4, Chapter 8, The Quidditch World Cup
"The stadium where the Quidditch World Cup is being held has had Muggle-Repelling Charms placed on every inch of it. Whenever a Muggle has been near to the Quidditch Stadium during the year leading up to the Quidditch World Cup, they have suddenly remembered urgent appointments and have had to dash away."