Saffron is an aromatic, colorful spice that flavors Spanish paella, Italian risotto, and numerous Middle Eastern and South Asian dishes. It is also the most expensive spice in the world. The delicate yellow-orange saffron threads (i.e., stigmas) must be handpicked from the eponymous crocus, ideally on the day the flower blooms.
The threads are then dried and often crushed. Since a little can go a long way, it's worth adding saffron to your spice rack, but make sure you buy it from a reliable source.