Single Data Rate (SDR) refers to a method of data transfer in which data is sent once per clock cycle. This means that for every tick of the clock, one unit of data is transmitted. SDR is commonly used in various types of memory, such as SDRAM (Synchronous Dynamic Random Access Memory), where it helps in maintaining a consistent flow of data. In contrast to Double Data Rate (DDR) technology, which transfers data twice per clock cycle, SDR is simpler and often slower. While SDR can be effective for certain applications, it is generally less efficient than its DDR counterparts, making it less common in modern high-performance systems.