A set of orthogonal arrows for indicating the X, Y, and Z axis in a three-dimensional space. This is often seen in 3D modeling programs as a tool to manipulate objects by moving, rotating, or transforming them. The arrows are usually red, green, and blue for X,Y, and Z respectively.
Besides arrows, the tool can have other appearances for the different functions mentioned above. One such variation is a set of circles, similar to a Gyroscope, for rotating objects.