The exclusive or operation - a logical function applied to binary bits, like AND, OR, and NOT - is a fundamental encryption technique. It is often used in stream ciphers, which are widely used in web browsers when connecting to secure web servers.
Whenever your browser establishes a “secure” connection to a web site, it encrypts the data. Traditionally, the browser and site use a stream cipher called Rivest Cipher #4 (RC4), although some sites use newer techniques.
Stream ciphers use a deceptively simple mechanism: you combine the plaintext data, bit by bit, with “key” bits, using the exclusive or operation. This is often abbreviated xor, and denoted by ⊕ - a circle with a cross.