SSL/TLS
SSL stands for Secure Socket Layer, and it is used to establish an encrypted link between a web server and a web browser to enable secure communications. TLS, in simple terms, is a newer version of the SSL protocol.
In short, SSL/TLS are a group of security protocols that provide secure communication over an insecure network. This is further illustrated in the following use cases.
Scenario 1 – A man-in-the-middle attack–storing credentials
In the following diagram, we can see that a user is sending their username and password in plaintext to a Web Server for authentication over a network.
There is an Attacker sitting between them doing a MITM attack and storing all the credentials he finds over the network to a file:

Scenario 2 – A man-in-the-middle attack–integrity attacks
In this scenario, a user has requested for a payment of $100 from a payment server. The Attacker who is sitting in the middle has altered the contents (the email address field) from [email protected]
to [email protected]...