The Enhanced Serial Multi-Modem Windows driver is a software component that enables communication between a computer's operating system (such as Windows) and serial multi-modem hardware devices, typically used for dial-up modems or other types of communication devices that operate over serial ports (RS-232, for example).

These modems are often used in older systems or in applications that require multiple simultaneous modem connections, such as for faxing, data transmission, or legacy communication protocols. The "Enhanced" version of the driver may provide additional features or optimizations for better performance or more advanced functionality compared to standard modem drivers.