A line is formed by the continuous movement of a point, and a plane is formed by the continuous movement of a line. Lines can be straight or curved, and planes can be flat or curved.

Shapes that lie entirely within one plane, such as triangles and circles, are called plane figures, while shapes that do not lie within a single plane, such as pyramids and cylinders, are called solid figures. Both plane and solid figures are composed of points, lines, and planes, which are the fundamental elements of geometric shapes.

Points and lines also appear when two shapes intersect. When a line and another line or a line and a plane intersect, the resulting point is called an intersection point. When two planes intersect, the resulting line is called an intersection line.

As shown below, there are infinitely many lines passing through a single point , but only one line passes through two distinct points and . Thus, two distinct points determine a unique straight line.

The line passing through and is represented as or simply as line .

A ray starts at point and extends infinitely in the direction of point .

A line segment includes points and and all points in between.

It represents the shortest path between and , and the length of is the distance between points and .

If there is a point on the line segment such that point is called the midpoint of .

An angle is a figure formed by two rays and starting from a common point . This angle is denoted as , , or simply or .

The vertex of the angle is , and the two rays and are the sides of the angle. The size of is the amount of rotation from one side to the other around vertex .

When the two sides of an angle and form a straight line, the angle is called a straight angle and measures .

An angle measuring is called a right angle, and it is denoted with a small square symbol.

When two straight lines intersect, they form four angles, , , , and . Among these, the pairs of angles that are opposite to each other, such as and , or and , are called vertically opposite angles.

The sizes of vertically opposite angles are always equal.

When two lines and intersect at a right angle, they are said to be perpendicular, and this is denoted as .

If a perpendicular line passes through the midpoint of a segment , is called the perpendicular bisector of .

For a point not on line , the point of intersection of line and the perpendicular from is called the foot of the perpendicular from to .

The segment is the shortest distance between and , and its length is the distance from point to line .