A V8 isolate is a separate JavaScript execution context created by the V8 engine. It gives each script its own runtime state, including objects, globals, and memory-managed data, so code can run without directly sharing JavaScript state with other code in the same process.
In cyber security, isolates matter because they are often used to sandbox untrusted scripts inside Node.js applications, plugin systems, and automation tools. They reduce accidental data sharing, but they are not the same as an operating-system sandbox: the code still runs in the host process, and native bindings, callbacks, or boundary-handling bugs can create escape paths. Attackers look for flaws that let data or control cross the isolate boundary, turning limited script execution into host-level compromise. Defenders use isolates for separation, but should pair them with least privilege, strict API exposure, and stronger containment when real untrusted code is involved.