Tribal tattoo designs are probably one of the most popular forms of tattoos in the world. These are generally known as designs traditionally used in the Pacific Islands and Africa.
Cultures who employs this tattoo style did not get them because they looked cool. They got them because they believed there was a certain power attached to the tattoo. Some tribes use elaborate tattoo designs as a way to signify a boy becoming a man and outcast those who are not willing to take part in this tattooing tradition. Other use them as protection in battle or as a signal of great warriors.
Tribal tattoos are recognizable by their dramatic use of aggressive dark lines in jagged symmetrical shapes spread throughout the skin. Tribal tats are most often done in simple black and skin tones but in the western world they are often infused with color to enhance the overall look. Whereas other tattoo styles attempt to represent a specific object, tribal tattoos seem far more concerned with the feel and meaning rather than what it specifically looks like.
Typical examples of modern tribal tattoo designs are arm or leg bands that seem to have become the most popular tattoo design over the last 5-10 years. These designs are typically only black but many artists have been using subtle shading or even inclusion of a less abstract design such as butterflies or dragons within a tribal design.
source: http://www.tattoopictureshop.com/tattoo-designs/tribal-tattoo.html