Asafetida is used is used essentially only in Indian cooking. It has a strong onion-garlic flavor. It is the resinous gum from a giant fennel called ferula. It is dried and sold as whole tears, whole lumps, crushed tears, or, most popular, ground tears
Asafatida is native to Iran and Afghanistan. It has been used for more than 2000 years. It was often used in Roman cooking and arrived in India via the Moghul empire.
Asafetida is a milky sap that is harvested from three species of Ferula, a giant fennel. Just before it flowers, the stems are cut and earth is scraped away to expose the large taproot. The taproot is cut and the milky sap exudes and hardens into a reddish brown (looks similar to brown sugar). Sunlight will spoil the liquid, so the process must be covered.
Asafetida should be used sparingly and fried lightly before adding to a dish. It can be used anywhere garlic would be appropriate and can be rubbed on the grill before cooking. It is used in some curry powders and on meats and vegetables.
Herbs and Spices by Jill Norman
http://www.food.com/about/asafetida-355
http://theepicentre.com/spice/asafetida/