Certificate Chain
The ordered sequence of certificates from a server's leaf certificate up through one or more intermediate CAs to a trusted root, used by clients to verify trust.
A certificate chain is the path from a server's leaf certificate to a root CA the client already trusts, usually through one or two intermediate CA certificates in between. The server is responsible for sending the leaf plus all intermediates during the TLS handshake; only the root must already be in the client's trust store. A missing or wrong intermediate is a classic deployment bug: it works in Chrome (which can fetch intermediates via AIA) but breaks in older clients, curl, and many SDKs. Tools like SSL Labs and `openssl s_client -showcerts` expose exactly which certs the server hands over.