My understanding is that jitter refers to essentially stochastic variation of an ideally isochronous/periodic process or signal. You might say "the event is supposed to occur exactly every 1 second; in practice we observed jitter of +/- 50 milliseconds," referring to the RMS (1-standard-deviation estimate) of a sample of inter-event durations. Wikipedia has a nice article: https://en.wikipedia.org/wiki/Jitter

In the context of video, I think the most common use of "judder" is about the deterministic and periodic variation in timing that occurs when content of one frame rate is shown on a different-rate display. The most common situation is a "3:2 pulldown," where 24 frame-per-second film content is adapted to a 60 field-per-second or frame-per-second video signal. This is done by repeating one film frame for 3 video fields/frames (so 3/60 seconds), and then the next film frame for 2 video fields/frames, then the next one for 3, then 2, then 3, then 2, etc. (2/5 = 24/60 so it works out on average.) That repeating variation in frame duration or number of repetitions is seen as "judder." With a cinema projector or recent TV, you don't have this; the frames are shown 1/24 s apart and with an equal number of flashes each. But on an older 60 Hz TV, you'll have judder.

(I've also seen "judder" occasionally used to refer to the stuttery motion that comes from showing 24 fps content on a sample-and-hold display, like an OLED [without black-frame insertion] or a "good" LCD that just shows each frame with constant brightness for the entire 1/24 s and then almost-instantly switches to the next frame. But I don't think this is the correct usage.)