At first glance, the translation of entidad appears obvious, and indeed, it is usually translated as "entity." Note, however, that Spanish expresses the common legal phrase "any person or entity" without using this word. In Mexican legal Spanish, you will see toda persona física o moral and in Argentine legal Spanish toda persona natural o jurídica. Both of those phrases mean "any person or entity."
Entidad also has a hidden meaning. It is an elevated synonym of importancia. Thus, for example, the phrase un vacío legal de cierta entidad means "a fairly significant gap in the law." Un problema de cierta entidad is "a fairly significant problem" not a "certain entity's problem."