Fan-out refers to the number of output lines that may be connected to a logic, chip, circuit or device.
The number is limited because the circuit or fan-out unit in question must provide the necessary driver power. In addition, if the maximum fan-out is exceeded, the then very low output impedance in connection with the pull-up resistor of the driver no longer reaches the high state of the logic signals, so that the subsequent devices are no longer able to evaluate the signals. For example, if the fan-out of a logic circuit is 10, then ten identical load units can be connected to the output like inputs.
Interconnect technologies at chip level can be implemented using wafer level packaging(WLP) as fan-out wafer level packaging( FO-WLP).