Secure Sockets Layer (SSL)
SSL, or Secure Sockets Layer, is a standard security technology for establishing an encrypted link between a server and a client—typically a web server and a browser, or a mail server and a mail client. This encrypted connection ensures that all data passed between the web server and browsers remain private and integral. SSL is an industry standard and is used by millions of websites in the protection of their online transactions with their customers.
Originally developed by Netscape in 1994, the protocol was designed to address the lack of security on the early internet. While SSL versions 2.0 and 3.0 have been deprecated due to vulnerabilities, they paved the way for TLS (Transport Layer Security), which is the modern and more secure version of the protocol. Despite the shift to TLS, the term SSL remains the most common way to refer to this type of Cryptography. The implementation of these protocols is facilitated through Digital Certificates, which are issued by a trusted Certificate Authority.
A core component of the protocol is the SSL Handshake, a process where the two communicating parties exchange public keys, verify identities, and generate session keys for Symmetric Encryption. According to Cloudflare, this process happens in the background without interrupting the user experience. You can find more technical details regarding the deprecation of older versions in RFC 7568 from the IETF.