Set membership refers to the relationship between an element and a set, indicating whether the element is part of that set. For example, if we have a set 1, 2, 3, the number 2 is a member of this set, while the number 4 is not. This concept is fundamental in mathematics and helps in organizing and categorizing objects. In set notation, membership is often denoted using the symbol ∈. For instance, we can write 2 ∈ 1, 2, 3 to express that 2 is a member of the set. Conversely, we use the symbol ∉ to indicate that an element is not part of a set, such as 4 ∉ 1, 2, 3.