It acts similiarly to Excel's ISNUMBER function. If the specified value is a number it returns true, in all other cases it returns false.
Usage
ISNUMBER(value)
Arguments
value
Input the number for it to evaluate if it is number? Works on vectors/arrays as well.
Value
first example returns true as it is a number. Second example returns false as it isn't a number, it's a string. Function will always return logical class.