A dried seed that comes from the fennel herb, fennel seeds look like cumin seeds, only greener, and have an aniseed flavour and a warm, sweet aroma. For cooking, green seeds are optimal.
The seeds and leaves of the fennel plant both have a licorice flavor, although the flavor of fennel is milder and somewhat sweeter than anise. Fennel seeds are the primary flavor component in Italian sausage. They're also used in spice mixes such as Chinese five spice and the Indian panch poran.
Fennel seeds are actually a spice, although the leaves, stalks and roots of the plant are known as a herb. Today fennel and fennel seeds are popular in Northern and Southern European cuisines, as well as in Chinese and Indian cooking, where they are often included in spice blends.