What is a labour union?

A labour union is fundamentally an organization of workers that is created to advocate for their collective interests in negotiations with employers. This representation often involves discussions on various workplace issues such as wages, working conditions, benefits, and job security. By organizing collectively, workers gain a stronger voice compared to negotiating as individuals, which enhances their bargaining power with employers.

This answer illustrates the core function and purpose of a labour union. They serve to protect workers' rights and advance their interests in a unified manner, making it clear why this option accurately describes what a labour union is. The other choices present definitions that do not encompass the primary role of a labour union in advocating for workers' rights and negotiating with employers.