An SSL (Secure Socket Layer) or TLS (Transport Layer Security) certificate is a digital certificate that authenticates a server (most often a web server) and encrypts the data exchanged with it. The data is thus exchanged in confidence between two actors whose identity is known. The data exchanged cannot be spied on or altered by a third party: confidentiality and integrity.
Download this document “5 minutes to understand: SSL / TLS certificates” on Nameshield’s website.