Normal closure refers to the concept of the smallest normal subgroup of a group containing a given subset. This mathematical term has several synonyms. One possible synonym is the normal subgroup generated by a set. Another is the normal hull of a set. One could also use the term normal completion. In topology, normal closure can be referred to as the normal cover or normal envelope. Some authors use the term characteristic closure as a synonym for normal closure, especially in the context of field theory. Regardless of the terminology used, normal closure remains a crucial concept in many areas of modern mathematics.