Senior is a term used in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 to describe a student

Student

A student is a learner, or someone who attends an educational institution. In some nations, the English term is reserved for those who attend university, while a schoolchild under the age of eighteen is called a pupil in English...

 in the 4th year of study (generally referring to high school or college/university study).

High school

In the United States, the 12th grade

Twelfth grade

Twelfth grade or Senior year, or Grade Twelve, are the North American names for the final year of secondary school. In most countries students then graduate at age 17 or 18. In some countries, there is a thirteenth grade, while other countries do not have a 12th grade/year at all...

 is usually the fourth and final year of a student's high school period and is referred to as senior year. In the England and Wales, anyone in Senior school/ High School (Year 7 - Year 11) can also be known as a senior. In Scotland, it is Year 8 onwards.

Higher education

In the US, the final year of a student's education towards a bachelor's degree

Bachelor's degree

A bachelor's degree is usually an academic degree awarded for an undergraduate course or major that generally lasts for three or four years, but can range anywhere from two to six years depending on the region of the world...

, typically the fourth year, is known as the senior year.

Intercollegiate athletics

In college athletics

College athletics

College athletics refers primarily to sports and athletic competition organized and funded by institutions of tertiary education . In the United States, college athletics is a two-tiered system. The first tier includes the sports that are sanctioned by one of the collegiate sport governing bodies...

, a student in their final year of eligibility is known as a senior.