An SSL certificate is essential for websites as it encrypts the data transferred between a user's browser and the server, enhancing security. This encryption helps protect sensitive information, such as login credentials and payment details, from potential eavesdropping or hacking attempts. Websites with SSL certificates display a padlock icon in the address bar, indicating trustworthiness to users and improving the site's credibility. Additionally, SSL certificates positively impact SEO rankings, making them a vital consideration for businesses seeking to enhance their online presence and safeguard user data.