In the United States education system, a senior in high school refers to a student in the fourth and final year of high school education). The twelfth grade is the final year of secondary school in most parts of the world, including the US, and is typically the last year of formal or compulsory education. Students in the twelfth grade are generally 17-18 years old, and on rarer occasions, can be 19 years old. In Canada, students generally enter their Grade-12 year when they are 16 or 17 years old, and they generally graduate high school at 17 or 18 years old. The terms freshman, sophomore, junior, and senior are used to describe what year of school someone is in, with senior referring to the fourth and final year.