1, four-digit classification: that is, a classification with four digits as a numerical level.

2. Numbers refer to writing numbers in a row side by side, and each number occupies a position. These positions are called numbers.

3. In geometry, a figure consisting of a point on a straight line and a part beside it is called a ray.

4. The length of the line segment connecting two points is called the distance between these two points.

5. Angles can be divided into acute angle, right angle, obtuse angle, right angle, rounded corner, negative angle, positive angle, upper angle, lower angle and 0 angle, which are 10 respectively.