40GBASE-X Ethernet signalling refers to a set of Ethernet standards that enable data transmission speeds of up to 40 gigabits per second (Gbps). This technology is typically used in high-speed network environments such as data centres and enterprise networks. The '40' in 40GBASE-X signifies the data rate in gigabits per second, while 'BASE' indicates that it is a baseband signal, meaning the signal is transmitted in its original form, without modulation. The 'X' is a placeholder for a variety of factors including the type of physical medium, the transmission distance, and the wavelength used. 40GBASE-X Ethernet signalling can be implemented over several different physical media, including copper and optical fibre. The specific type of media, along with the distance over which the signal can be transmitted, is indicated by a suffix. For example, 40GBASE-SR4 signifies short-range multimode fibre capable of transmitting signals up to 150 meters, while 40GBASE-LR4 signifies long-range single-mode fibre capable of transmitting signals up to 10 kilometres. 40GBASE-X Ethernet signalling utilises parallel transmission, where multiple lanes of data are transmitted simultaneously to achieve the high data rates. This contrasts with serial transmission, where data is sent bit by bit along a single path.