Physically not considered as a color, it is what you see, or rather don't see, when light is totally absorbed by the object. But it can be considered the essence of everything there is.
How the color is made: historically, black pigments were made by crushing charcoal, burnt wood, or burnt animal bones. In RGB color space black has a very memorable hex number (#000000) and RGB components: 0 red, 0 green and 0 blue. And in CMYK color space it has its own channel - black, which have its full value 100% with zeros for the rest.
History: black and white are the oldest known and used colors, you can see black drawings from the dawn of humanity till now. In ancient Greece, it had bad connotations as it was connected to evil and the underworld. Yet, in ancient Egypt it has positive connotations as it was considered a color of fertility and protection. Today it is a sign of simplicity and sophistication. And any civilization had its own consideration for the color black.
Color in Action
Today black is a sign of seriousness, simplicity and slickness. Yet, if misused it can be a color of sadness, depression and down mood.
Colors that go with Black
The question of is black (or white for that matter) is a great match for a particular color, is not a question to be asked. As almost all of the color spectrum a good fit for both of the opposites. The only thing that matters is the contrast (for some usecases) between the chosen color and black, which require the use of a light color!
Black Color Palettes and Schemes
For a homogeneous look and feel use black with white and grays in between. Yet to add a dynamic look and feel for your graphic, use a vibrant color, or two matching colors. And to emphasize the black use it as a base color, though it can be used as an accent in the case of using analogous color palettes of any color.
Backgrounds and Seamless Patterns
Well, speaking of backgrounds, black is the background of the universe itself. It can be used as a background for almost all kinds of visuals. Dark or black wallpapers is probably the most used black-related keyword in google. Patterns, especially geometric of night-sky-inspired can't be more beautiful!