Types of Angles
Every angle you'll encounter fits into one of five main categories based on its size. An acute angle measures less than 90°, like the corner of a slice of pizza. A right angle measures exactly 90° and forms that perfect square corner you see everywhere.
When angles get bigger, they become obtuse angles, measuring more than 90° but less than 180°. Think of opening a book wider than 90°. A straight angle measures exactly 180° and looks like a straight line, whilst a reflex angle opens even further, measuring between 180° and 360°.
Adjacent angles share a common side and vertex - they're basically neighbours sitting next to each other. Complementary angles are best mates because their measures always add up to exactly 90°. Supplementary angles are also partners, but they add up to 180°.
Quick tip: Remember "C" for Complementary = 90° and "S" for Supplementary = 180°. The alphabetical order matches the size order!