Hard to define perhaps, but I like this one from a dictionary.
An imagined event or sequence of mental images, such as a daydream, usually fulfilling a wish or psychological need.
This seems to sum up my spanking fantasies. I have no idea if other mammals have fantasies but it strikes me that the ability to place oneself in another world, without any apparent effort, is probably an attribute of the human mind.
I can fantasize at the drop of a hat. Just put me in an environment where I feel that I am effectively alone and I can extract a fantasy from the menu in my head and play out whatever spanking scenario I wish.
I don't have to be alone in a bed; I can do it on a train, a plane or in a car travelling with a driver, when I am pretending to be asleep.
I love it.
It is a splendid way to pass the time.
The scenes are perfect in every detail.
Mistresses are approachable but strict, attractive girls who I am about to spank are loving and submissive. The strokes of the cane can be harsh or the hand spanking can be affectionate.
The fantasy can be lengthy, extending into several chapters, or it can be short and I can move into a completely different scene within seconds.
Oh, and there is another advantage - the outcome is always the one you thought it would be - no surprises here in fantasy world.