11. Line segment: A line segment has two end points with a definite length.
2. Ray: A ray has one end point and infinitely extends in one direction.
3. Straight line: A straight line has neither starting nor end point and is of infinite length.
4. Acute angle: The angle that is between 0° and 90° is an acute angle.
5. Obtuse angle: The angle that is between 90° and 180° is an obtuse angle.
6. Right angle: The angle that is 90° is a Right angle.
7. Straight angle: The angle that is 180° is a straight angle.
8. Supplementary angles: If the sum of two angles is 180° then the angles are called supplementary angles. Two right angles always supplement each other. The pair of adjacent angles whose sum is a straight angle is called a linear pair.
9.Complementary angles: If the sum of two angles is 90° then the two angles are called complementary angles.
10. Adjacent angles: The angles that have a common arm and a common vertex are called adjacent angles.
11. Vertically opposite angles: When two lines intersect, the angles formed opposite to each other at the point of intersection (vertex) are called vertically opposite angles.
12. Perpendicular lines: When there is a right angle between two lines, the lines are said to be perpendicular to each other.
13. Parallel lines: The line is called a transversal, that which intersects two or more lines (not necessarily parallel lines) at distinct points.
