Jitter as defined by NIST is the “short term phase variation of the significant instants of a digital signal from their ideal positions in time”. As an oscillator’s signal gets multiplied and filtered, the jitter gets multiplied and filtered as well, and a system’s timing budget can quickly disappear. Therefore, designers need to possess a good understanding of timing jitter and how it will affect their system design. This paper provides a short introduction to some of the terminology surrounding clock jitter and gives an overview of the approaches used to specify and measure jitter in timing devices.