Spot color uses a method of specifying and printing colors in which each color is printed as its own ink. In contrast, process color printing layers four inks (yellow, magenta, cyan and black) together to produce color. When a brand's color identity is critical companies often produce advertisements using a combination of process and spot colors. This is commonly called 4+1. 4 representing the process inks, and 1 representing the brand's specific spot color.
Spot color printing is effective when the printed matter contains only one to three different colors, but it becomes prohibitively expensive for more colors. You can also use tints of a spot color to achieve the appearance of using more colors without the expense of additional inks.
There are a number of color specification systems for specifying spot colors, but Pantone is the most widely used. These colors are also commonly referred to as PMS Colors (Pantone Matching System).