# What is TLS?

Transport Layer Security is a protocol used to protect communications between endpoints.

Website: https://zenshield.com/glossary/tls

Canonical URL: https://zenshield.com/glossary/tls

Page reviewed: 2026-09-09

Transport Layer Security is a protocol used to protect communications between endpoints. In web browsing, it underpins HTTPS. Encryption, integrity checks and authentication work together; the exact properties depend on the protocol version and configuration.

## A practical example

When you visit an HTTPS service, the browser checks information presented during connection setup. A certificate warning means the browser cannot accept the connection under its normal checks. It is a reason to investigate, not an extra installation step.

## What to check

Read the actual warning before taking action. Check the full hostname, device clock and whether you intended to open that service. On an organization-managed device, ask its IT team about its configuration instead of installing an unfamiliar certificate. Keep private account details out of a screenshot you send for help.

## What it does not tell you

TLS does not turn every destination into a trustworthy business. A VPN tunnel and a website’s TLS session are also distinct. Do not assume that a normal VPN operator can automatically read all HTTPS message contents just because traffic uses its route.

Read the [technical reference](https://developer.mozilla.org/en-US/docs/Web/Security/Defenses/Transport_Layer_Security) for the underlying definition. For a connection that is failing now, use the [troubleshooting guide](https://zenshield.com/help/connection-problems). To choose an app, follow the [VPN selection worksheet](https://zenshield.com/learn/choosing-a-vpn).

## Sources
- https://developer.mozilla.org/en-US/docs/Web/Security/Defenses/Transport_Layer_Security