Terpenes are the fragrances that you smell in flowers and plants that have beneficial effects. In a similar way that aromatherapy works by inhaling the scent of certain terpenes in nature has been associated with a boost in emotional well-being. The sweet, floral scent of the terpene linalool, for instance, found in lavender, has a calming, sedative effect. Limonene, a terpene found in citrus fruits and peppermint, has a mood-elevating effect, while pinene, found in sage and conifers has been shown to aid in alertness and memory retention.

Many common Terpenes found in cannabis are:
Borneal – also found in cinnamon and wormwood is said to have a calming effect.
Caryophyllene – also found in black pepper, clove and cotton
Cineole/Eucalyptol – also found in rosemary and eucalyptus is said to centers/balances.
Delta 3 Carene – also found in rosemary, pine and cedar resin
Limonene – also found in citrus fruit, rosemary, juniper and peppermint
Linolool – also found in lily and citrus
Myrcene – also found mangoes, hops, lemon grass, verbena and mercia. It is said to possess relaxing effects.
Pinene – also found in rosemary, sage and eucalyptus and is said to increase mental focus
Sabinene – also found in oak trees, tea tree oil, black pepper and carrot seed oil and is said to be an effective antioxidant.
Terpineol – also found in flowers, citrus, apple/orange blossoms and is used in perfumes and soaps.

There are many many more terpenes and their uses and effects have not been fully documented.