Traffic exchanges, also known as hit exchanges and start exchanges, are a very simple means of driving traffic to a website.
Being in a traffic exchange is like being in a club. You surf, using a specially designed "surf bar" unique to the traffic exchange in question, and view the other club member's websites. Every time you view a website you get a credit, or a point, and these are exchanged for visitors who view your website. Normally there is a "ratio" involved and - for free members - it is often one return visitor for every two websites that you view.