RECENT: Defining Our Field - what is 'classical music' to us, why are we involved and what can we learn from our differences? Read John Dante Prevedini's essay, watch the panel discussion and make your own comments.
Rosin is solidified resin taken from pines and other plants and trees, mostly conifers. It's made by heating liquid resin to evaporate the liquid.
In music, it's used in blocks or cakes by string players, who rub it on their bow hair to help make their instruments' strings vibrate clearly. Some types of rosin are mixed with gold, iron, silver, tin or beeswax to modify the friction and (possibly) the tone produced.