An organised group of citizens acting together and seeking to obtain the control of government is a

A political party is an organised group of citizens who share similar political ideas and come together with the primary objective of winning control of government through elections. This distinguishes political parties from all other forms of association.

A civil society organisation advocates for specific causes and holds government accountable, but it does not seek to win governmental power itself. A labour union represents the collective interests of workers in matters of employment, wages, and working conditions. A student union represents students' welfare within an educational institution. None of these bodies contests elections or aims to form a government.

The defining characteristic that separates a political party from other organised groups is its explicit goal of obtaining and exercising the power of government, typically by nominating candidates, contesting elections, and forming or joining a government if successful.