A 502 Bad Gateway error is an HTTP status code that indicates one server on the internet received an invalid response from another server. This error commonly occurs when a server acting as a gateway or proxy cannot get a valid response from an upstream server. Causes can include server overload, network errors, misconfigured firewalls, or temporary outages. For users, it typically means the website is temporarily unavailable or experiencing issues. For administrators, resolving a 502 error often involves checking server logs, network connectivity, and configuration settings to identify and fix the underlying problem.