The data rate is the number of bits per second used to transmit a video and audio stream. The ATSC specification calls for 19.25 Mbps data rate for a high-definition terrestrial transmission. However, some cable/satellite broadcasters use a lower data rate because most of these transmissions are movies without a lot of high-speed motion. Generally, a higher data rate will translate to better video quality, especially with high-speed motion scenes. For content such as movies, you most likely would not be able to tell the difference between a data rate of 12 Mbps and one of 19 Mbps. For content such as sports, you probably would see a difference between those data rates.