802.1X is the port-based network access control framework — requiring authentication before granting network access. Components: Supplicant (client), Authenticator (switch/AP), Authentication Server (RADIUS).
802.1X is the mechanism; RADIUS is the protocol; EAP is the authentication method. Enterprise Wi-Fi uses WPA2/3-Enterprise + 802.1X + RADIUS for per-user authentication. Without 802.1X, any device can plug into a network port or connect to Wi-Fi with the PSK.