SSL stands for Secure Socket Layer. Like TLS (which stands for Transport Layer Security), SSL is a security protocol that operates between a browser and a Web site. It provides confidentiality and data integrity by means of cryptographic techniques and, when used with a third-party-issued certificate it can report trustworthy information to one party about the other party. Typically, this is used to provide the browser and its user with trustworthy information about the Web site.
Cryptographic techniques provide confidentiality and data integrity protection for messages passing in either direction between the browser and the Web site. This prevents Internet Service Providers that handle the messages in transit from viewing or modifying the contents of the messages. It also mitigates attacks on the DNS, such as DNS cache poisoning and on the HTTP caching system, such as HTTP response splitting.