"judder" is a sniglet or neologism [aka "portmanteau"] formed from 2 or more words being morphed together to form a novel word, such as "giant+enormous=GINORMOUS." in judder’s case it is a combo of shudder and jitter, describing for the first time the psychovisual phenom of flicker in 24 frame-per-second projected motion picture material esp. when further distorted by the telecine process lacking proper 3:2 pulldown. i myself can’t easily watch large-screen movies for that reason, i get a queasy feeling akin to seasickness, when i see that shake magnified a jillion times up there.