Classifying angles

Straight angle is a straight line. It has measure 180°
At the picture angle ABC is straight angle

Right angle is half of straight angle. It has measure 90 °
At the picture angle DEF is right angle.

Acute angle is less than straight angle. It has measure less than 90°
At the picture angle LMN is acute angle.

Obtuse angle is bigger than straight angle and less than straight angle. It has measure bigger than 90° and less than 180°.
At the picture angle XYZ is obtuse angle.

Reflex angle is bigger than straight angle. It has measure bigger than 180°

Angle pairs

Adjacent angles are called angles like a and d, or a and b or b and c or c and d Sum of adjacent angles are equal to straigth angle(180°), so a = c and b = d.

Vertical angles are a and c or b and d. Vertical pair of angles are equal i.e. a = c and b = d

Let's have two parallel lines intersected by third line. Angles m and q or n and r or o and s or p and t are called corresponding. They have the same measure.