Origin Shield
An intermediate caching layer between CDN edge nodes and the origin, so a cache miss at many edges results in one origin request rather than many.
A global CDN has hundreds of points of presence. Without a shield, a cache miss at each of them produces its own origin fetch — so a cold or newly-purged object can generate hundreds of simultaneous origin requests, which is a thundering herd caused by the CDN itself.
An origin shield designates one location as the parent cache. Edge misses go to the shield; only the shield's own misses reach the origin.
The benefits: dramatically higher origin offload, protection during purges and deployments, and a smoother origin load profile. The costs: an extra hop for requests that miss at the edge, and the shield becoming a component whose location matters — it should be near the origin.
The same idea appears as request coalescing within a single cache, and as a hierarchical cache in CDN terminology.