People, who are not familiar or interested in geocaching are called "muggles". They are non-geocachers. The term "Muggle" is based on the Harry Potter series where muggles a non-magical peoples.
You don't want muggles discovering your cache! Since muggles do not know or not respect that geocaching is a game, they could destroy your geocache or throw it away.
Always try not to draw attention to yourself when seeking a geocache. You could arouse curiosity of outsiders. They could come over and ask what you're doing. Or, even worse, they come over AFTER you have left and attempt to find whatever seems to be there and destroy it. They could also call the police because you are doing something suspicious. So, if there are to many muggles around the geocache's location: come back later!
Be prepared to answer questions from muggles. If a muggle comes over either you can offer a plausible excuse or you just admit that you're geocaching. Explain it to them and always try to protect the geocache!