Workers are separate JavaScript execution contexts that run tasks off the main browser thread. They let web pages do background work such as parsing data, handling messages, or processing large computations without freezing the user interface. Common types include Web Workers and Service Workers, both designed to isolate work from the page’s primary scripting thread.
In security terms, Workers matter because they add another execution boundary inside the browser. Bugs in worker handling can affect isolation, message passing, memory management, or access to browser objects, and those weaknesses may be useful in exploitation chains. Defenders pay close attention to worker code because it often processes untrusted web content at high speed and with less visible oversight than page scripts. Hardening worker APIs, patching browser updates quickly, and limiting unnecessary worker use all help reduce risk.