WebSocket protocol is a new network protocol based on TCP, which enables the creation of a persistent connection between a browser and a server through a single handshake. Since there is no need for repeated handshakes between the browser and server, bi-directional data exchange between the two becomes much simpler. Specifically, WebSocket in MQTT refers to establishing a connection using WebSocket first and then communicating over the WebSocket channel using the MQTT protocol, i.e. MQTT over WebSocket, which is mainly used for connections in the browser environment.
WebSocket over TLS/SSL means to add TLS/SSL encryption to WebSocket protocol communication. In this way, the communication is secured from eavesdropping and tampering.