() Operator (C# Reference)
In addition to being used to specify the order of operations in an expression, parentheses are used to perform the following tasks:
Specify casts, or type conversions.
double x = 1234.7; int a; a = (int)x; // Cast double to int
Invoke methods or delegates.
() operator cannot be overloaded.
For more information, see Casting and Type Conversions.
For more information about method invocation, see Methods.
C# Language Specification
For more information, see the C# Language Specification. The language specification is the definitive source for C# syntax and usage.