MIMO stands for "multiple-input-multiple-output" and is part of a wireless standard that describes how Wi-Fi routers with multiple antennas can handle data streams for optimal performance when various devices are connected. Manufacturers denote a typical configuration as 3x3:3. The first number indicates the number of transmit antennas, the second number represents the number of receive antennas, and the last digit represents the maximum number of spatial data streams the radio can use. As is so often the case, more antennas and data streams results in higher performance.