Sun-dried tomatoes are ripe tomatoes which are dried in the sunlight to remove most of the water content from them. 

Sun dried tomatoes were originally created in the tile roofs as a way to store fresh tomatoes for the winter. They may also be preserved in olive oil, along with other ingredients such as rosemary, basil, tomatoes, dried paprika  and garlic. 

Nowadays sun-dried tomatoes are used more as a gourmet ingredient. You can eat sun-dried tomato halves as they are. Quite some people would soak it to remove some salt content, and to make it soft. Sun-dried tomatoes can be used in a wide variety of recipes, for example, to make tomato sauce.