A set is a collection of distinct objects, considered as an object in its own right.
For example, the numbers 1, 3, and 5 are distinct objects when considered separately, but when they are considered collectively they form a single set of size three, written {1, 3, 5}.
The concept of a set is one of the most fundamental in mathematics. Elementary topics from set theory such as Venn diagrams are taught at a young age, while more advanced concepts are taught as part of a university degree.