Collective is a word that describes a group of people acting together. A prom might turn into a smashing success through the collective efforts of the student body.
The word collective indicates a group, and is often used in opposition to the efforts or will of an individual. Your neighbor who is the only one on the block who refuses to mow her law? She's going against the collective. A commune is a type of collective living situation, in which several families might live together and contribute for the benefit of the whole. If you work well with others, then you appreciate how collective efforts can often result in better results.