Much has been debated on this topic since the appearance of the digital era (photoshop and others). Many "purists" claim that anything done to the original image is an "enhancement", but to be honest, such enhancements have been made by protographers long before computers existed.
From the moment you choose a wide angle or a tele, or black and white film or as simple as the use of a filter, you are "altering" reality. Darkroom techniques too did their share of enhancements, from contrast altering to burning and dodging under the enlarger. The use of chemicals to "crack" emulsions, shift colors (sepia and selenuim toners for example) and even the basic scissor and glue technique, all mean "enhancing" or "altering reality". Think about double exposures
When the subject of "digital enhancements" shows up, 99% of the time they refer to altering reality to a point that no longer resembles the original image.
To me (and many in the graphic arts community) a digitally enhanced image is one that lacks something that existed in the original, or has something that was not part of the original. This includes of course, retouching (cloning out things) or embedding objects from other images into one image.
Of course, digital enhancements include the use of software plugins (canvas, oil painting, distort, etc) even if done over a virginal image, no matter if it was done with digital camera or scanner from negative or slide.
Contrast enhancement by sections, color shifts and balancing and cropping even done digitally, are not considered "digital enhancements"
In matter of competition (contests = photo) you better get the straight rules upfront to avoid surprises. Not everyone thinks the same.
Robert