In photography today, a high-key image is one that is almost entirely very bright with very little or no dark shadows present. This is usually a creative decision made by the photographer, in order to create a certain mood in the image.
A bright, “airy” image most often creates a light, pleasant mood, as opposed to a dark, shadowy image which most often creates a dramatic, romantic, or even scary mood. Hope you like it as much as I do.