CDMA stands for Code-Division Multiple Access which is a digital wireless technology. It competes with other similar digital wireless technologies such as GSM.
CDMA is considered "spread spectrum" technology which means that information contained in a particular signal are spread over greater bandwidth.
CDMA, as compared to other technologies such as GSM, has no limit to the amount of users who share one cell tower. Instead, additional users can connect until the tower determines that call quality for the entire network would be too low.
CDMA networks operate in the 800 and 1900 MHz frequency bands mainly in the Americas.