A straight angle is an angle that measures exactly 180 degrees. It is formed when two rays or lines extend in opposite directions from a common point creating a straight line. Straight angles are important in geometry and are used to define other types of angles and shapes.

Lines and angles are key concepts in geometry. A line extends infinitely in both directions and angles are formed when two lines meet. Types of angles include acute right obtuse and straight angles. Understanding lines and angles is essential for solving geometric problems and creating basic geometric shapes and figures.