Often misconstrued as a positive attribute given to a foodstuff. What is really means in science is "calories" i.e. fat and sugar. Cue the energy bar. It seems like a healthy option when compared to chocolate bars but most energy bars contains just as much, if not more, calories as a chocolate bar! Shock, horror!
Also, energy is used to describe caffeine containing products e.g. energy drinks. These are often laced with sugar and super high amounts of caffeine. Most energy drinks also contain interesting ingredients e.g. Guarana and Taurine which haven't yet been confirmed to be safe for human consumption.
Moral of the story- read your labels (back and front). Also, if it's about nutrition, ask a Dietitian!