Queuing process is a class of random process es describing phenomena of queue formation. The term “queue” here is an abstract entity, which reflects the most common features of various types of real-life queues: traffic jams, queues to football matches, queue of e-mail messages on a server which are to be sent, etc.
The queuing process 
characterises the length 
of the queue – i.e. the number of units in the queue in the current moment, time . Statistical description of a queuing process implies knowledge of its probability distribution 
– the probability of finding exactly units in the queue.
Models based on a Poisson process, Erlang distribution are often used in the queueing theory.