A social poster is one with a social message. Through images, social posters can be used to denounce injustice, something abusive, or to celebrate some achievement. The final goal is to make people think about something in particular, and if possible, react about it.
One of the most critical things in our society now is the lack of job for many individuals. Lots of people loose their jobs for a very long time, starting a chain that ends up with the collapse of their lives and themselves. Someone loses his job, then cannot pay the bills, cannot pay the house, cannot pay his food, and eventually becomes alienated from the society, and from himself. Others have jobs that are very little rewarded, and also collapse, in a different way. So our job is that foot that we cannot loose, like in the image below.
See it in http://www.posterfortomorrow.org/en/gallery/view/38113