Intersection: Two straight lines intersect at a point, which we call intersection. In contrast, we call these two straight lines intersection. Perpendicular: When two lines intersect at right angles, they are said to be perpendicular to each other. Parallel lines: In the same plane, two lines that do not intersect are called parallel lines, and their relationship is called mutual parallelism.
High number refers to the complicated part of mathematical objects and methods compared with elementary mathematics. In a broad sense, all mathematics except elementary mathematics are advanced mathematics, and some call algebra, geometry, simple set theory and logic in middle school intermediate mathematics, which is the transition between elementary mathematics in primary and secondary schools and advanced mathematics in universities.