Design pattern that isolates critical resources to prevent total system failure. Like having watertight compartments on a ship so one leak doesn't sink the entire vessel.
E-commerce sites use bulkhead patterns to ensure payment processing continues working even if product catalog systems fail.
Bulkhead is an architecture/design pattern, not a single cloud service. On any provider, you implement it by isolating resources (compute pools, queues, databases, thread pools, rate limits, and network boundaries) so a failure or overload in one area cannot exhaust shared capacity and take down other critical functions.