Ya'll need to be careful... One or two responses almost contained useful information not wrapped up in dogmatic hyperbole.
To the OP:
"apochromatic" is a term which is supposed to indicate the lens design is corrected for all three major wavelengths, leading to less color aberrations. It's also become a marketing term meaning "Very Expensive Lens".
"aspherical" is a lens design that is intended to increase sharpness across the field of view, as opposed to spherical designs which are sharpest at the center. Also frequently means "more expensive".
ED is referring to the actual glass used, I'll borrow B&H's description:
How much each of these aspects contributes to the quality of your photo depends entirely on your subject, composition, lighting, film, etc.. It's typically more important in digital and especially digital astrophotography, where APO designs using ED glass will return much sharper results. With large-format, as you might have noticed from earlier responses, it's far less critical-- in fact, a number of LF photographers would prefer lots of fall-off, loss of sharpness, etc., and disregard any phrase with "color" in it.
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