Thai "Nam prik"  (sometimes spelt Nahm Phrik) is a general term used to describe a  spicy paste  which is prepared in a variety of ways.  It's Thailand's equivalent to the Indian "Chutney" or Indonesian "Sambal" and is served as an condiment with rice, vegetables, meats, poultry and fish but can also be served as a dip.

The basic ingredients of Nam prik are some type of fish paste, garlic, fresh chilies, fish sauce and lime juice however they vary from region to region and can include garlic, dried fish, tamarind pulp, fruit such as green mango and nuts.

Chilies although relatively new to Thailand now plays an essential role in Thai cuisine in the form of Namprik (chili paste or chili water).

There is a complete food cultre around NamPrik - thai literature and phrases incorporate this phenomonen, how to eat it (its tastes best when eaten with fingers and not cutlery), what kinds of food go well with various varieties of namprik etc.. Certain varieties, for example, go with smoked catfish or deep fried mackerel.

Stripped down to its most basic elements, a nam phrik will usually encompass all of the four Thai tastes: salty, sweet, spicy and sour.
Sour additions to NamPrik - tamarind, lime juice, mango, solanum, gratawn (santol), or other fruits.
Salty additions - salted eggs or fish, fish sauce, fermented soybeans in the mix, but the most popular form of chili paste is probably Ka Pi, which features dried shrimp.
Sweet additions - palm sugar, onions

Variations
Na Rok: Thai Chili Paste Na Rok is a dry chili paste. Thai chilli paste Na Rok is good with fresh or steamed vegetable
Tom Yum Sour Soup Paste - this is not technically a nam prik.  It is a paste for Tom Yum soup by adding this to chicken stock or coconut milk.  This paste howevet could be used to flavor stir fry's and used as a nam prik for cooking.
Plaa-raa: a mud-like, unfiltered, unpasteurized fish paste with a smell and taste even more pungent than that of kapi.
Plaa-tu:  is made up from dried shrimp paste, garlic, green chili, shrimp paste, fish sauce, lime juice and palm sugar.
Nam plaa phrik: a small saucer of fish sauce mixed with thinly sliced chilies, and sometimes sliced garlic and lime juice, a rough equivalent to the salt shaker in western countries.
Nam Phrik Num: The main ingredient is phrik num, long slender green chilies that are almost exclusively used in this particular dish.
Nam Phrik Ong: chili paste with minced pork and tomatoes.
Nam
Chilli Paste with Basil - these are nam prik sauces in which gresh herbs have been added and they make convenient seasoning sauces for cooking   
Asian Chili Sauces : Chili Garlic, Sambal Oelek and Siracha are commom Asian sauces that may be used as Nam Prik 

Namprik can also play a central role in Thai cuisine starting with choosing the namprik first and buliding the menu around the namprik chosen. For example, namprik toa jeaw (chili paste with fermented soybeans) is usually served with grilled ma-khue yao (eggplant), smoked catfish, or deep-fried snake heads. Meanwhile, Namprik ma muang (chili paste with mango) or namprik ma kham (chili paste with tamarind) ought to be accompanied by salted eggs, deep-fried dried beef, and grilled salted fish to help soften the sourness of these varieties of namprik.

Namprik advantages are many - it is easy to incorporate herbs with it encouraging people to eat more fresh herbs daily, it is low in fat, it is very satisfying so one does not overeat.