The symbol "∅" represents the empty set in mathematics, which is a set that contains no elements. It is a fundamental concept in set theory, indicating the absence of any items or numbers. The empty set is unique and is a subset of every set. The notation "1" denotes a set containing a single element, which in this case is the number 1. This set is not empty, as it includes one specific item. Sets can contain various types of elements, including numbers, letters, or even other sets, and are often used to group related items in mathematics.