A 'dinker' is a cutsie name for an animal that looks interesting, and has colors or markings that a person thinks just MIGHT be due to a genetic mutation.
In other words, it's an animal that you will 'dink around with' to see if you can prove it to be a new morph.
It is not of any known morph, it just looks like it might have the potential to be a new morph.
Dinkers are considered to be 'interesting normals' until they are proven otherwise. Many morphs were discovered when someone picked up a 'dinker', and bred it out, and proved it to be genetic.
Normal ball pythons are extremely variable in color and appearance, which is why most dinkers do not 'prove out'--they turn out to not be a morph, but just an interesting normal, after all.
Dinkers get some respect, because a lot of the new morphs that are being discovered now are VERY subtle. Morphs such as Russo, Mystic, Trick, and Spector are very difficult to differentiate from normal ball pythons--someone noticed a little 'something' about them, and decided to try to see if it was genetic, and there you go.