National Council of Teachers of Mathematics
The Math Forum: Ask Dr. Math: The Origins of Conic Sections
Dr. Math, in reply to a student question, gives background information on the origin of conic sections. Links also are included for further information.
Wolfram Research
Wolfram Math World: Eccentricity
This site explains eccentricity, the quantity defined by a conic section to determine its type of conic section. Has links to related topics.