Betel nut ( 槟榔 ), also known as pinang or Areca nut, is the seed of the Betel Palm, a species of palm which grows throughout the Pacific, Asia, and parts of east Africa. It is a medium-sized tree growing to 20 m tall, with a trunk 20-30 cm diameter. The leaves are 1.5-2 m long, pinnate, with numerous, crowded leaflets.

Dried and half-cut Betel nuts are given as gifts and offerings, while the betel nut powder is flavoured with spices and chewed for pleasure.

The most important active principles of betel nut are arecaine and arecoline, alkaloids which are comparable to nicotine in its stimulating, mildly intoxicating and appetite-suppressing effects on the mind. It also contains the alkaloids arecaidine, arecolidine, guracine (guacine), guvacoline and a number of others that have not yet been studied extensively.

Betel chewing is a part of many Asian cultures, and preparation techniques vary from region to region. The nut is either slivered or grated, often flavored with spices according to local tradition and usually wrapped in a betel leaf (note: betel leaf comes from the betel pepper plant, Piper betle, which is not botanically related to the betel palm, Areca catechu), along with some lime (calcium oxide or calcium hydroxide) to better extract the alkaloids. Some people also chew tobacco with betel nut. After about 20 minutes of chewing, the fibrous residue which remains of the nut is spat on the street, where it remains visible due to its characteristic bright red dye. Trails of bright red sputum lining the sidewalks are a sure indication of the popularity of betel chewing in an area.

Regular betel chewing causes the teeth and gums to be stained red; however, it may also reduce cavities. Betel chewing is addictive. The International Agency for Research on Cancer (IARC) regards betel nut to be a known human carcinogen.

Powdered betel nut is a constituent in tooth powders. Other medicinal uses include the removal of tapeworms and other intestinal parasites by swallowing a few teaspoons of powdered betel nut, or by taking tablets containing the extracted alkaloids.