Here is an example of a derivative.
Farmer Larry plants 100 acres of wheat every Spring. Each Spring he also agrees to sell that wheat at a certain price on a certain date in October, to a certain person. Farmer Larry has just entered into a derivatives contract.
There is probably a good chance your Utility bill is a derivative contract every month. If you agree to pay a fixed monthly rate, like I do, regardless of your amount of usage, then you have probably entered into a derivatives contract.
Yes there are derivatives and there are derivatives.
The ones you refer to are the simpliest of derivatives.
Enron was dealing in the most complex of derivatives; derivatives even Enron hardly understood.
That's why they're going belly up.