What does () stand for? 

()

A bracket, as used in British English, is either of two tall fore- or back-facing punctuation marks commonly used to isolate a segment of text or data from its surroundings. Typically deployed in symmetric pairs, an individual bracket may be identified as a 'left' or 'right' bracket or, alternatively, an "opening bracket" or "closing bracket", respectively, depending on the directionality of the context. There are four primary types of brackets. In British usage they are known as round brackets (or simply "brackets"), square brackets, curly brackets, and angle brackets; in American usage they are respectively known as parentheses, brackets, braces, and chevrons. There are also various less common symbols considered brackets. Various forms of brackets are used in mathematics, with specific mathematical meanings, often for denoting specific mathematical functions and subformulas.

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