essential element
essential element (elemento esencial)
words needed to tell which person or thing is meant, so they are not set off by commas.
Example
Workers who finish early may leave. (Only those workers may leave, so there are no commas.)
In Spanish
essential element (elemento esencial) — palabras necesarias para saber de qué persona o cosa se habla; por eso no van entre comas.
Workers who finish early may leave. (Solo esos trabajadores pueden irse; por eso no hay comas.)