The word Nazarite comes from the Hebrew word Nazir, meaning "consecrated", or "separated (from others)". Another possible root for this term is the word "Nezer", which stands for "Crown". Indeed, a Nazarite's head is crowned with the long locks that symbolize this sacred separation. A Nazarite might perform austerities, often symbolic in nature.
The Book of Numbers, traditionally ascribed to Moses, sets more specific guidelines for Nazariteship. For a minimum of 30 days, a Mosaic Nazarite is told to keep the hair uncut, avoid consumption of wine, vinegar and any other "fruit of the grapevine", and avoid ritual defilement through contact with corpses. The Book of Numbers also outlines the sacrifices such a Nazarite would need to make at the temple as certain points of the vow.
Other forms of Nazariteship are mentioned in biblical texts (such as Samson), and it's likely that this is a tradition that goes back to before the times of Moses.
Other famous biblical Nazarites are John the Baptist and Samuel the Prophet.
A more modern example of the Nazarite Vow can be found in Rastafarian ideology. As per an adaptation of the rules set by Moses (and possibly influenced by the Sadhus of India), many Rastafarians let their hair grow into long dreadlocks.