SSL is the special cryptographic technology to protect the connection between browser and website (web-server to be precise). The usual nonsecure connections use HTTP, while the secure connections are marked with HTTPS. The web server used for e-store must have this technology to protect and keep in privacy customers' data during the order placing and payment.
The web servers should have the special SSL certificate issued by the Certificate authority. The SSL certificates differ by validation type, features, guarantees, prices and active time.