The relative condition number is defined here:
Numerical Linear Algebra - Google Book Search
In an example, I have that f(x) = exp(x). What is the relative condition number here?
I assume it is x*exp(x)/exp(x) = x. Is this correct?
Well, the site you link to gives the "relative condition number" as and further notes that if f is a real valued function of a single real variable, that reduces to . In your example, f(x)= exp(x), f'(x) is also exp(x) so they cancel and your are almost correct- the relative condition number is |x|.