The colour portion of a video signal.
Chrominance refers to the colour information in a television picture. Chrominance can be further broken down into two properties of colour: Hue and Saturation.
Chrominance Signal
The high frequency portion of the video signal which is obtained by quadrature amplitude modulation of an (NTSC) 3.58 MHz subcarrier by R-Y and B-Y.
Color Difference Signals
Signals used by colour television systems to convey colour information in such a way that the signals go to zero when there is no colour in the picture. R-Y,B-Y, 1 and Q are all colour difference signals.
References
Kodak: A Concise Glossary for the Non-Technician