V8 bytecode is an intermediate compiled form produced by the V8 JavaScript engine before code is fully executed. V8 uses it as part of its normal pipeline to speed startup and execution in browsers and Node.js.
In security work, V8 bytecode matters because malware can ship in a compiled .jsc-style form instead of readable JavaScript. That makes quick triage, deobfuscation, and signature writing harder, since analysts may need version-matched tools and runtime debugging to recover behavior. Attackers use this to hide logic in loaders, stealers, and droppers, while defenders look for bytecode-aware reversing, suspicious bundled runtimes, and unexpected script execution in Node.js or browser-related environments.