Meta noise

Meta noise refers to inaccurate or irrelevant metadata. This is particularly prevalent in systems with a schema not based on a controlled vocabulary, such as certain folksonomies.
Examples:

misspelled tags, or tags with multiple spellings
obviously inaccurate or joke tags
On systems open to large user groups, tags which are understood by only a minority of users.
Hidden benefit

Although the existence of meta noise may initially appear to detract from the value of metadata generally, meta noise allows less popular tags to be defined and used by a minority of users without damaging the validity or cohesion of what the majority of users would consider to be the most relevant or accurate metadata, thus actually increasing access to content.

Meta noise

Hidden benefit