直布罗陀巨岩，磐石山（位于地中海西南端直布罗陀港城附近的一处悬崖，象征十分安全或坚如磐石）a high cliff at the south-western edge of the Mediterranean Sea, near the town and port of Gibraltar. When people say that sth is like the Rock of Gibraltar, they mean it is very safe or solid.
When I invested my money with the company I was told it was as safe as the Rock of Gibraltar.