Is Santa Real? I think it is an interesting question given the Christmas/Advent season. Maybe not for the reasons you might think. There are so many 'Santa' traditions and depictions, varying from country to country and family to family, that one could spend a great deal of time on what is even meant by 'Santa'. My answer on whether Santa exists or not will arguably hold regardless of the iterations or riffs on him.
For most people (or scrooge-y adults), the knee-jerk answer is "of course Santa is not real. He is a legend that represents the spirit of Christmas, generosity, benevolence, child-like wonder and hope..." and so forth. When we get down to brass tacks, if we framed the question in a very clear way, something along the lines of "is there an individual, spatially extended, animate, rational being occupying space and time corresponding to the name and properties of Santa Claus?" then probably most people would answer in the negative. Or at least they would say there are no good arguments or evidence to think this is the case. In any event, I would argue it is wrong to say "Santa does not exist" or to say "Santa is not real". As I alluded to in my admittedly terse definition above, the real question should be "In what way does Santa exist?"
Santa most certainly does exist in a particular way. He 'exists' at least in terms of what some philosophers would say is a 'being of reason'. By this, I mean that Santa is a complete concept or idea, commonly understood, within the intellect of rational creatures. If this were not the case, we could not speak about Santa, make movies and songs about him, and children could not come to expect gifts (or coal) from him. Santa exists in the same way other fictitious characters do, like Batman or Superman. The human intellect is able to apprehend and reason with and about certain universal ideas. These 'ideas' are not merely subjective constructs of each individual person. Rather, they are like the concept or idea of a triangle or square, or a number or letter. These ideas are conjoined together in various ways, which is how we are able to speak to one another about them and each person perfectly understands the other. When I say there are nine reindeer, you understand the concept of nine in the same way as another person. Again, if this were not the case, there would be no intelligible communication with one another.
The meaning of Santa Claus is understood by people who are familiar with the terms and properties making up what is said about him. In perhaps a more technical philosophical sense, Santa has an essence but does not have an individuated act of existence. Here I am adopting a fairly standard Thomistic distinction between essence and existence (as Aquinas does in De Ente et Essentia with the example of comparing a man and a phoenix). To press the point a bit further along these lines, we might say that Santa exists as an apprehended essence within individuated acts of existence (of the human essence). We know 'what' Santa is, and 'that' he is not except that which is within my intellect and yours. I argue that the same essence can be within your intellect and mine. As Aquinas says, we can both understand what a phoenix is without knowing whether one is flying around or molting (or whether we have reason to think one is). Likewise, we can understand what Santa is without knowing whether he is riding a sleigh or making toys at the North Pole.
Now, we may have good reasons to think that there is no man riding a flying sleight at night on Christmas Eve and that there is no toymaking factory within the Artic ice. Despite this, we should not say that Santa does not exist or that he is in some way not real. Doing so threatens to reduce our language and concepts to unintelligibility. It also quite possibly threatens to bring sadness to those who cherish the virtues of Santa and his mission. Far better to bring a smile