1, the meaning of a set is that the specified objects become a set together, which is called a set for short, and each object is called an element. For example, the collection of Grade One and Grade Two, then all the students in Grade One and Grade Two form a collection, and each student is called the element of this collection.

2. The representation of sets usually uses uppercase letters to represent sets and lowercase letters to represent elements.

3. Set and its elements are two different concepts, which are given by description in textbooks, similar to the concepts of points and lines in plane geometry.

4. The elements in the set are deterministic, different and out of order.

5.Set has two meanings: all eligible objects are its elements; As long as it is an element, you must sign the condition.