Trigonometry is the branch of mathematics that deals with triangles and relationships between sides and angles. It was originally developed to solve geometric problems involving triangles. Key concepts in trigonometry include trigonometric ratios such as sine, cosine, and tangent that relate angles and sides of a right triangle. Trigonometry is used in many fields including architecture, engineering, astronomy, music and more. It allows calculations of heights, distances, and positions that are important for applications like building design, navigation, and satellite positioning.