Trigonometry is the study of right triangles and the relationship between the sides and angles of those triangles. Astronomers of the 3rd century noticed these relationship and created what we call trigonometric functions (sin, cos, tan) which are now used to describe the cyclical phenomena in fields such as physics, mechanics, music, astrology, ecology and biology. A prevalent use of these functions can be found in surveying of land for the purposes of creating accurate maps and divisions of land.
In high school, trigonometry is usually taken in 11th grade and is studied mostly as pure mathematics without much application to the real world unless taken in an honors setting. Along side algebra, a student can learn how the functions can be used in parallel with algebraic equations. With the Common Core now taking place of the regents, students taking trig can expect more emphasis on algebra which can take some strain off the more complex inverse functions and their uses. The primary concern of most students is the applications of sin, cos, and tan on right triangles.