電轟雷轟 is built from two interleaved pairs — 電 and 雷 (both "lightning/thunder") bracketing a doubled 轟 ("roar... roar") — which makes it the most sonically self-descriptive of all six original Thunder Breathing names. Say it out loud and the repeated -ou sounds mimic the very rumble the compound names; nothing else in the style's naming set doubles a kanji for emphasis this way.
VIZ compresses that four-kanji thunderclap of a name into the tidy two-word "Rumble and Flash," sacrificing the doubled-roar structure but keeping the sound-plus-light pairing that runs through the whole style (compare "Thunderclap and Flash" for Form 1) — a consistent house strategy of one "sound" word plus one "light" word for each translated form name, regardless of how much internal repetition the original Japanese carries.
Dramatically, this is the technical peak of Kaigaku's demonstration, and the line that follows it is the whole duel's thesis statement: "I became a demon and surpassed Thunder Breathing!!" Sixth Form is less a technique in its own right than the exact moment Kaigaku declares victory — right before Zenitsu answers not with a stronger demon body, but with a brand-new human form no one has ever seen.