The ABCD parameters, also known as chain, cascade, or transmission line parameters, are electrical circuit parameters used to represent two-port networks. They are commonly used to analyze the cascade or series connection of multiple two-port networks, such as transmission lines, transformers, filters, and small-signal transistor models. The parameters are defined such that when used to represent cascaded two-ports, the matrix notation follows the order the networks are drawn from left to right in a diagram.