What exactly is the parameter of a curve?

For the longest time, I'd assumed that the curve parameter was a range from a value of 0 to the curve length. However when I tried to evaluate the curve at the parameter of its length, as seen in the screenshot, it's nowhere near the end. In fact, the parameter at the end of the curve which I found with the Crv CP is completely different to what I would've expected. Can someone explain parametrisation of curves, and by extension - surfaces, should it follow a similar principle?