Flat Foot Technology® has been awarded not one, but two patents. Yeah, kind of a big deal. You really need to ride an Electra to feel it, but the overall benefit is comfort and control. It provides an upright, relaxed seating position with proper leg extension that allows you to plant your feet flat on the ground whenever you want or need to.
Derailleur or "D" refers to an external shifting mechanism. It consists of a chain, multiple precision sprockets and a derailleur to "derail" the chain from one sprocket to another. It allows for quick transitions and more gearing options. Just remember to pedal while shifting and you're good to go!