An SSL certificate is an X.509 certificate that is used to provide authentication, privacy and integrity for a secure connection. Although the acronym refers to Secure Sockets Layer, the SSL protocol is deprecated and the certificates are more commonly used for Transport Layer Security (TLS) connections.

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Sure, you can still buy them (and there are companies out there that would just love to sell them to you!), but their usefulness has now descended from "barely there" to "as good as non-existent". This change has come via a combination of factors including increasing use of mobile devices, removal of the EV visual indicator by browser vendors and as of today, removal from Safari on iOS (it'll also be gone in Mac OS Mojave).