Asynchronous Transfer Mode (ATM) is a protocol developed for broadband ISDN that supports high data transmission rates. It uses fixed-size cells called ATM cells that are 53 bytes long, with 5 bytes for header and 48 bytes for payload. ATM cells allow data to be organized into logical connections identified by Virtual Channel Identifier and Virtual Path Identifier values. These logical connections support quality of service guarantees and efficient transmission of data, making ATM well-suited for real-time multimedia applications.