The term often is used to describe impacts on a cache hunt. "I couldn't look for the cache because there were too many muggles nearby."
The term muggle has been around for decades and means many things in different environments; in the early part of the last century, among musicians, muggle was a reference to drugs (specifically marijuana) and drug users.
More recently, the term has enjoyed renewed popularity, mainly due to its use in the Harry Potter series by J. K. Rowling, where it refers to non-magical people.
Muggles are generally harmless. However, care should be taken to avoid revealing the location of a cache in their presence. Sometimes caches are muggled (vandalized by non-geocachers).
Some geocachers do not like to use the word muggle (see surrep), but it is rapidly becoming the norm when refering to those not informed about our hobby.
The term muggle has sometimes been applied to some geocachers themselves. Because there are multiple geocache listing sites, geocachers who hunt caches listed on only one site may not be aware of the existence of caches listed on other sites. Someone in a park, unaware of the existence of a nearby cache, is considered by some to be a muggle, even if they are avid geocachers otherwise.
Synonyms and related words include: