Using Escape Slash

This is an example of using escape slash: "Learning PHP is fun!"

Not Using Escape Slash

This is an example without escape slash: "Learning PHP is fun!"

One is the escape (backslash), which prevents the termination of a string by a special character. This includes the quotation marks, which are used to denote the start and end of a string. In the first example, the double quote is not the end of the string due to the backslash. If you didn't include the escape slash, PHP would see the quotation mark and think the string ended there, causing a syntax error (wrong string formatting).