Also known as available bit rate (ABR). In asynchronous transfer mode (ATM), a class of traffic that does not require guarantees of network access, but rather can deal with time slot access on an as-available basis. Bursty LAN traffic and e-mail are examples of best-effort ATM traffic. ATM also defines constant bit rate (CBR) and variable bit rate (VBR) traffic classes. See also ATM, CBR, e-mail, LAN, time slot, and VBR.