The LT PCI Modem is a type of dial-up modem that uses the PCI interface to connect to your computer. It enables your computer to connect to the internet via a telephone line. The "LT" in the model name often refers to a specific chipset (such as Lucent Technologies) used for these modems. The LT PCI Modem Windows driver is the software that allows Windows to recognize and communicate with the modem, enabling it to work correctly for internet connections and other functions.