TLS (Transport Layer Security) is a protocol that facilitates privacy and security for communications over the Internet by encrypting data between web applications and servers. It ensures encryption, authentication of communicating parties, and integrity of data. TLS is needed to protect sensitive information transmitted online from tampering or eavesdropping by third parties. It works by encrypting communication from both the client and server sides to securely transmit data. Users can check if a connection is secure by looking for a padlock icon in their browser and viewing details like the TLS version used.