Surface energy describes the excess energy at a material's surface relative to its bulk. Practically, it predicts wetting: a liquid spreads on a solid when the solid's surface energy exceeds the liquid's surface tension.
This is why the same coating behaves completely differently on different substrates. Metals and glass have high surface energy (hundreds of dynes/cm) and are easy to wet. Polyolefins have low surface energy (29-31) and resist wetting entirely. PET sits in between at around 41-44.
Surface energy can be raised by corona treatment, flame treatment, plasma treatment or chemical priming, or lowered accidentally by contamination — silicone, slip additives and oils are all effective at destroying adhesion.