Given the task definition and input, reply with output. In this task, we ask you to rewrite a sentence in simple English without changing its general meaning. Essentially, you want to make the sentence easier to read by using simpler words, utilizing more straightforward sentence structures, and omitting non-essential information etc.

A voluntary group or union ( also sometimes called a voluntary organization , common-interest association , association , or society ) is a group of individuals who enter into an agreement , usually as volunteers , to form a body ( or organization ) to accomplish a purpose .

A voluntary association or union is a group of individuals who voluntarily enter into an agreement to form a body ( or organization ) to work together for a purpose .