Someone told me that jitter is defined as how much the return time in ms of an ICMP is varying:
Pinging Some host [x.x.x.x] with 32 bytes of data:
Reply from x.x.x.x: bytes=32 time=66ms TTL=122
Reply from x.x.x.x: bytes=32 time=68ms TTL=122
Reply from x.x.x.x: bytes=32 time=63ms TTL=122
Reply from x.x.x.x: bytes=32 time=67ms TTL=122
The above ping request offers little jitter...if the time in ms differed more wildly it would have a high rate of jitter.
High jitter implies that there is some random or intermittent component between you and your endpoint that is causing packets to be retransmitted or otherwise delayed.
For example a collision on a wifi connection would cause the packet to be lost and then it would need to be retransmitted. This would cause a random delay of some number of milliseconds as the transmitter would pause briefly to ensure "clear" air in order to make sure that the packet transmits cleanly. If another device causes another collision then packets get delayed further.
These kinds of "expected noisy" networks that actively detect and work around a collision are generally fault tolerant, but depending on how many devices are fighting for air time there can be a significant delay in a successful transmission.
This is one of the many causes of jitter, and every link can have different properties.
