In asynchronous transfer mode (ATM), one bit in the cell header that identifies the priority level of the cell to determine the eligibility of that cell for discard in the event of network congestion. Applications such as LAN-to-LAN traffic and e-mail are tolerant of loss. Applications such as real-time voice and video are highly intolerant of loss. See also ATM, cell, congestion, e-mail, header, LAN, real-time, traffic, video, and voice.