TLS (Transport Layer Security) is a cryptographic protocol used to secure communications between servers, their nodes, and clients.
Although TLS, SSL, and TLS/SSL are often used interchangeably, the Vertica documentation always uses TLS to reference the protocol. Some Vertica parameters and components use SSL, and in these cases the documentation uses SSL to reference them, but these too can be categorized under the TLS umbrella.
Enabling TLS is a multi-step process. You can check the status of your security configuration with SECURITY_CONFIG_CHECK.