Trigonometry is the study of angles. It is a branch of mathematics that is used for algebraic solving in geometry. With the knowledge of trigonometry anything from calculus to vector algebra can be solved.
Trigonometry is used in finding out the heights of tall objects like mountains, trees, etc. The tool used in trigonometry for this purpose is called clinometer.
"There is perhaps nothing which so occupies the middle position of mathematics as trigonometry."-J. F. Herbart