A students' union, student government, student senate, students' association, guild of students or government of student body is a student organization present in many colleges and universities, and has started appearing in some high schools. In higher education, the student union is often accorded its own building on the campus, dedicated to social and organizational activities of the membership. In the United States, student union many times only refers to a physical building owned by the university with the purpose to provide services for students without a governing body also referred to as a student activity center. Outside the United States this refers to a representative body.

Depending on the country: the purpose, assembly, method and implementation of the group might vary. Universally the purpose of students' union or student government is to represent fellow students in some fashion.

In some cases students' unions are run by students, independent of the educational facility. The purpose of these organizations is to represent students both within the institution and externally, including on local and national issues. Students' unions are also responsible for providing a variety of services to students. Depending on the organization's makeup students can get involved in the union by becoming active in a committee, by attending councils and general meetings, or by becoming an elected officer.

A police officer (also known as a policeman or policewoman, and constable in some forces, particularly in the United Kingdom and other Commonwealth nations) is a warranted employee of a police force. In the United States, "officer" is the formal name of the lowest police rank; in many other countries "officer" is a generic term not specifying a particular rank, and the lowest rank is often "constable". Police officers are generally charged with the apprehension of criminals and the prevention and detection of crime, and the maintenance of public order. Police officers may be sworn to an oath, and have the power to arrest people and detain them for a limited time, along with other duties and powers.

Some police officers may also be trained in special duties, such as counter-terrorism, surveillance, child protection, VIP protection, and investigation techniques into major crime, including fraud, rape, murder and drug trafficking.

Responsibilities of a police officer are varied, and may differ greatly from within one political context to another. Typical duties relate to keeping the peace, law enforcement, protection of people and property, and the investigation of crimes. Officers are expected to respond to a variety of situations that may arise while they are on duty. Rules and guidelines dictate how an officer should behave within the community, and in many contexts restrictions are placed on what the uniformed officer wears. In some countries, rules and procedures dictate that a police officer is obliged to intervene in a criminal incident, even if they are off-duty. Police officers in nearly all countries retain their lawful powers, while off duty.