Technically, from what I understand, a "Zepp" is a 1/2WL wire end-fed with
1/4WL of parallel feedline. Of course any odd multiple of 1/4WL will work.
A "Center-Fed Zepp" is a one wavelength dipole usually fed with an odd
multiple of 1/4WL of parallel feedline to achieve system resonance without a
tuner.
An "Extended Zepp" is a 5/8WL end-fed antenna - same as the popular 2m 5/8WL
vertical.
An "Extended Double Zepp" is a 1.25WL center-fed dipole usually fed with a
matching section of ~1/5WL parallel line plus any number of 1/2WLs.
Technically, all Zepps are single-frequency antennas. You can use a "Center
Fed Zepp" on other frequencies but it is no longer technically a Center-Fed
Zepp. You can
use an End-Fed Zepp on other frequencies but it is no longer technically an
EDZ.
The balluns used in a lot of Zepps are really pretty inefficient. You're
much better, if at all possible, using a balanced-line tuner into a dipole
fed with open-line.
http://www.qsl.net/ta1dx/amator/practical_dipole_antenna.htm
Steve, K8SP