Solar sail is a propulsion technology based on light reflection.
A star or some other light source provides thrust through absorption or reflection of photons (so-called radiation pressure) by a large sail fitted onto the starship.
An interesting feature of solar sail technology is that the radiation pressure decreases proportionally to the gravity of the star, meaning that theoretically the provided thrust remains identical regardless of the distance to the star. An advantage over other methods of propulsion is that solar sail does not require fuel of any type to operate.
Thanks to the presence of tachyon eddies in their star system, Bajoran lightships were able to reach faster-then-light speeds and perform interstellar travel, though only out of their system. The Bajorans used solar ships as early as the 16th century, and continued to do so until as late as the 21st Century. (DS9: "Explorers")
External Links
The Cosmos I at Wikipedia