Michael Howard provides an explanation:
Invariably, when I ask people what Transport Layer Security (TLS) does, they say something like, “it protects my credit card info when I buy things online.”
The response is not incorrect, but it’s not the whole story, either, and let’s just ignore the server-side credit card protection requirements and PCI compliance for a moment.
TLS provide three security services, with an optional fourth.
Click through for those services and some of the ways we can improve our security posture when connecting to (or hosting!) a SQL Server instance.