Otherwise known as a digital certificate, an SSL certificate (Secure Socket Layer) is a form of internet security. Used for authentication purposes, an SSL certificate provides certain guarantees that when internet users log on to a certain site, the information they enter - such as credit card, debit card and Social Security numbers or other types of personal data - cannot be stolen by identity thieves or hackers. This is done via encryption. The business or website itself also gains protection through SSL certificates.
Businesses generally have to obtain an SSL certificate if they wish to sell online. Some of the more well-known SSL providers include Verisign, GeoTrust, Comodo, and GoDaddy, among others.