What makes tags so appealing is that they are:
1. User-contributed (the user determines what tags to apply to an item)
2. User-defined (the users determine what tag to apply to a concept)
There is a consensus-building process that seeks to answer "what is the
best tag for this concept / this item?" From the point of view of the
users, the answer is "whatever enables folks to find this concept / this item".
Criterion: by frequency
Tag frequency is a technique that systems have to make it easier for users
to find concepts and items tagged with those concepts.
