Skill is just the ability to do something well. It's why there's arguments on who is better than who all the time. If you just label something as skill, there can be a whole different varieties of what makes that someone skillful (all of which are subjective). However, if you define something first (as danny did) and then base skill on what is predefined, than that particular skill can be objective.
For instance, you can call the ability to win a skill. From this point, whoever wins the most is obviously the most skilled.
However, you can say it takes skill to make a sammich. Since the ability threshold for making sammiches is relatively low, it becomes a contest with a wide variety of tastes and pallets of the consumer that judge how skillful a person is at sammich making (ie subjective). You could have two excellent women sammiches side by side and several people will say sammich A was the best while others say sammich B is the best. Which woman is more skilled at making sammiches?
If their breasts are the same size, it's a subjective argument ;o
Though, to my original point I digress. You can argue that every game your skill goes up. You can become skilled at being predictable or skilled at reinforcing punishable habits just as much as you can refine skills of unpredictability and consciously removing bad habits.
Whether or not this self-definition of skill goes up with each match is something I could care less to argue.