Full-size frames, adult weight ratings and useful real-world range.
An adult e-bike is a full-size bike built for grown riders: frames sized for roughly 5'3" to 6'4", weight ratings in the 275 to 350 pound range, 26 to 29 inch wheels (or 20 inch on folders and fat bikes), and a battery big enough for real errands and commutes. The label exists mostly to separate these bikes from youth and compact models, but it also signals the basics a grown rider needs: enough motor to move an adult and cargo, brakes sized for that weight, and a saddle and cockpit that are adjustable over a meaningful range.
Within the adult category you will find every style — commuter, cruiser, fat tire, folding, cargo and mountain — so the decision is really about how and where you will ride. Flat North Texas neighborhoods and trails are forgiving; almost any 500W to 750W hub motor with a 48V battery handles them. Riders over about 220 pounds, or anyone carrying a child or groceries, should pay attention to the total weight rating and brake size. Taller riders should check the height range carefully, because many online e-bikes are one-size and fit best between 5'5" and 6'1".
Class matters for adults because it determines where you can ride and how fast. Class 1 and 2 (20 mph assist, with or without throttle) are accepted on most paths and trails; Class 3 (28 mph pedal assist) is faster for road commuting but restricted on many multi-use paths. Texas recognizes the three-class system; cities and trail managers may add their own rules, so verify locally. Sensible first adult e-bikes are Class 2 commuters or step-throughs with hydraulic brakes and a 500Wh-plus battery. If your bike has started misbehaving — cutting out, losing range, not charging — an E-Bike Assessment is the right first step.