The function "cosh(-x)" refers to the hyperbolic cosine of the negative of a variable x. The hyperbolic cosine function, denoted as cosh, is defined as (e^x + e^(-x))/2, where e is the base of the natural logarithm. This function is even, meaning that cosh(-x) is equal to cosh(x). This property of being even indicates that the graph of the hyperbolic cosine function is symmetric about the y-axis. Therefore, for any value of x, the output of cosh(-x) will be the same as that of cosh(x), reinforcing the idea that hyperbolic functions share similarities with their trigonometric counterparts.