set

is: a collection of entities (often, though not necessarily, numbers) that are defined by some characteristic which they all have in common, making them members or elements of the set, and which distinguishes them from entities that are not members of the set. [M1.2]

is exemplified: by the positive whole numbers. [M1.2]

is denoted: by listing the entities inside braces which signifies that they are elements (members) of the set. For example the set of non-negative whole numbers can be denoted by [M1.2]

has its membership indicated: by the symbol which means 'is a member of (a particular set)'. [M1.2]