Term Kind Topic What it is
Mutual TLS mTLS, Client Certificate Authentication protocol TLS & Certificates TLS in which both ends present certificates, so the server authenticates the client cryptographically rather than by a shared secret.
Server Name Indication SNI, TLS Host Extension protocol TLS & Certificates The cleartext hostname a client sends in its first TLS message, letting one address serve many certificates and letting a proxy route a session before it decrypts anything.