A Triad is a combination of 3 colors that are equidistant from each other on the color circle. It produces a high contrast effect while preserving ’harmony.’ Such a composition looks vibrant even when you use pale and unsaturated colours.
An easy to read diagram of different colour combinations and relationships. - Another brilliant diagram of colour relationships repinned from Ariana. Seeing as this one is all of them together, it might be easier to read.