This paper presents a discovery that the length of the entities in various
datasets follows a family of scale-free power law distributions. The concept of
entity here broadly includes the named entity, entity mention, time expression,
aspect term, and domain-specific entity that are well investigated in natural
language processing and related areas. The entity length denotes the number of
words in an entity. The power law distributions in entity length possess the
scale-free property and have well-defined means and finite variances. We
explain the phenomenon of power laws in entity length by the principle of least
effort in communication and the preferential mechanism