A trade union is a group of people who all work in the same kind of job and join together to help make sure that they get treated fairly at work and get the best wages and things like holidays and pensions. It's like a club for all the people who work in a particular kind of job. All the members of the union work together to try and make sure that their employers follow laws about treating workers well and that workers get higher wages and better working conditions. Whenever a worker joins the union, all the other members help to make sure that the worker is getting treated fairly and getting the same wages and benefits as everybody else.