M/M/1 Waiting Line
M/M/1 is Kendall's notation of this queuing model. The first part represents the input process, the second the service distribution, and the third the number of servers.
The M represents an exponentially distributed interarrival or service time, specifically M is an abbreviation for Markovian.
The M/M/1 Waiting line system has a single channel, single phase, Poisson arrival rate, exponential service time, unlimited population, and First-in First-out queue discipline.