Realism is a style that tries to recreate images as they would appear in real life. Realism typically lacks the bold outlines found in more traditional forms of tattooing and instead uses shading and color contrasts to render the image.
Realistic tattoos most commonly depict portraits or landscapes that mimic the fine detail of a photograph. Artists and tattoo collectors tend to prefer doing these pieces in black and grey, as it can be really difficult to capture the colors of a photograph and the tones of black and grey provide significant depth to a tattoo. The style is also called photo-realism and not all tattoo artists are able to master this style.