I ain't no jitter expert but all digital players must break the original signal, which is one continuous signal, into little bits and take a finite amount (44.1kHz or larger if oversampling is used) of samples from the original signal. If there is an error in the sample timing, such as irregular sampling intervals, they call it jitter. It was also a dance in the 1920's and is a lot of fun.
Sincerely, I remain