Solar wind is exactly what it sounds like, "wind" from light. Basically this phenomenon is based on the fact that the sun, or any other star, emits a stream of plasma that consists of electrons and protons traveling at very high speeds.
Recently there has been talk about figuring out how to harness this energy to create a spaceship that can travel long distances without having to use any fuel. This would be great for long journeys because it has no moving parts and no propellant and therefore would be very durable.
The only problem with this form of travel is that it is very slow. The pressure that the wind exerts is less than 1 newton per meter. However because its a space craft, if you get a large enough wing area and a long enough trip, the force created would accelerate the ship to a high speed but over a very long period of time.
Based on this, a spacecraft powered by solar wind would be possible, but is not the best way to get to mars in a lifetime.