A religious holiday episode which only mentions the not-overtly-religious trappings of the holiday, without the religion. Religion doesn't even crop up casually. This applies to all of the big Christian holidays such as Christmas and Easter, and also Jewish holidays such as Hanukkah, Yom Kippur, and Rosh Hashanah, as seen in Shalom Sesame, the Jewish American version of Sesame Street.
This does reflect Truth in Television somewhat, as these days there are plenty of people from Christian backgrounds who are not particularly religious but still celebrate Christmas and Easter with parties and gifts and chocolate, as well as some who aren't Christian at all but do the same. After all, few say no to free presents.
Contrast with Do They Know It's Christmas Time?.
C. S. Lewis wrote a couple of essays highlighting the commercialization of Christmas in the 1950s. In fact, this problem became a subject for concern very soon after the "old-fashioned" Christmas-as-we-know-it was invented in the 19th century.
Both averted and played with in The Vicar of Dibley. The title character is obviously well-aware of what Easter actually means, but one of her parishoners (a Cloudcuckoolander) was never told the truth about the Easter Bunny. When the old woman who usually filled this role dies, the vicar has a lot of explaining to do.
One of the "Two A-Holes" skits on Saturday Night Live featured the title characters in a live Nativity scene. At one point, the female a-hole picks up the baby Jesus doll and declares, "This baby doesn't look like Santa."
Having a Christmas-themed episode is common in Super Sentai seasons (which are usually nearing the end of their runs around this time).
On Peep Show, Jeremy has strong views on the right way to celebrate Christmas, which have nothing to do with religion and everything to do with being a Man Child who wants the holiday to feel familiar and safe. In what for him is the ultimate test of faith, he declines Mark's sister's proposition to have sex in the next room while the rest of the family eats dinner:
Jez: But Sarah, it's Christmas. Sarah: So? What, are you religious now or something? Do you believe in Jesus? Jez: No, of course I don't believe in Jesus. But I do believe in Christmas. I'm a Christmasist. [thinking, as Sarah exits] Wow, I did it! I resisted something for something else! That was... something! Mark, guess what! I was just offered sex, and I turned it down! Mark: Oh, well, congratulations. Jez:[proudly] I did it for Father Christmas. Mark:[thinking] God, look at him. He probably thinks Father Christmas died for our sins.
Semi-averted in FoxTrot. Commercial aspects of both Easter and (especially) Christmas are generally predominant, but the family is occasionally shown to go to church on those days. One memorable instance after Jason exults at length about his new, violent video game: "This is what Christmas is all about. You know, besides all that other stuff."
Andy: Jason and I will be at church, if anyone needs us. Jason: Mom! What makes you think they're even open today?!
The Christmas strips of Calvin and Hobbes concentrate on Calvin's attempts to behave so that he gets all the presents he asked for. One strip has Calvin doubting the existence of Santa Claus, and then Hobbes asks:
Hobbes: Isn't this a religious holiday? Calvin: Yeah, but actually, I've got the same questions about God.
When Bun-Bun sets out to become the King of All Holidays in Sluggy Freelance, he has to kill the previous leaders of the holidays to gain their titles and powers. To gain control of Christmas and Easter, he kills Santa Claus and the Easter Bunny, not Jesus.
The Peanuts special It's the Easter Beagle, Charlie Brown is an actual Easter example. A Charlie Brown Christmas nicely subverts this: Snoopy is only concerned with winning a house decoration contest, Lucy is more concerned with getting a nice tree than with the Christmas pageant, and Charlie angsts about how commercialized Christmas has become (in The Sixties, mind you). Later on, Linus reminds the whole gang about the holiday's true meaning by reciting part of the second chapter of Luke, in which the shepherds learn of Jesus's birth. This is actually what makes the show a classic — by going back to the real meaning of Christmas, it stood out in an increasingly commercialized world.
Ironically, it's now possible to decorate your house entirely with Peanuts-themed Christmas merchandise, including an entire line of plastic figures recreating the deeply spiritual moments of the special, and even a plastic replica of the tree that Charlie Brown picked out specifically because it was the only real tree in the lot.
The later Christmas-set Peanuts specials of The Nineties and the Turn of the Millennium are more focused on gift-giving, general winter activities, etc., but do acknowledge the religious side of the holiday. Two of them have the characters participating in Nativity plays/assemblies, and Sally wants to know who "the star" was that the Wise Men followed in Charlie Brown's Christmas Tales.
The Fairly Oddparents paint the Easter Bunny as a disgruntled "hard-boiled" figure who is envious of the big guy's popularity. The 'big guy' being Santa Claus : One episode revolved around all the other holiday mascots kidnapping Santa.
South Park plays this straight by making Mr. Hanky the Christmas Poo, a Christmas Spirit in the vein of Frosty the Snowman. There is an Easter Episode wherein the secret message behind the Easter Bunny, hidden from you by the eeevul Vatican, is uncovered.
Actually averted in the shorts thet preceeded the actual show, where Santa Claus and Jesus try to kill each other over who's the real Christmas deity, only to be presented with the message of what Christmas is about. Similarly, a couple of episodes in the main series do allude to the schism between religious Christmas and commercial Christmas.
In Elmo Saves Christmas, the Easter Bunny sells "Christmas Easter Eggs for Easter". There's nothing religious about any of the episode, whether Christmas or Easter.
In The Nightmare Before Christmas, all the holidays are in their secular forms, though, interestingly, Jack does refer to God offhandedly twice in "Poor Jack".
In the Futurama universe, Christmas (pronounced X-Mas) is less about religion and more about finding a good hiding spot from the killer robotic Santa who judges everyone to be naughty due to his standards being set too high. Except Zoidberg!
Also Played With during the show's Passover and Hanukkah episodes: the Biblical stories are recounted, but God is never directly mentioned, even though the various miracles occur. (Non-fatally, in the Passover example—a mysterious force is going to "take away" the firstborn.) There was a normal episode of the show based on Noah's Ark that did the same thing, claiming that Noah was just "told by the Heavens" (or something) of the coming Flood.
On Family Guy, when Lois discovers that she's Jewish and wants to put on a seder, Peter objects because it's Easter.
"In this house we believe in the Easter Bunny! He died for our sins in that helicopter crash..."
Japan at large practices the commercial holiday of Christmas, but only 2 percent of the population is Christian. Of course, they practice it somewhat differently than everyone else; one of their Christmas Traditions is eating Kentucky Fried Chicken, which is treated as something of a "special event" delicacy in Japan thanks to KFC's marketing and Japan's lack of turkeys.
Ironically, the feast day of the "original Santa Claus", St. Nicholas (or Sinterklaas in Dutch), is December 5th. In several Western European countries, notably the Netherlands and Belgium, this is the day when gifts are exchanged, usually replacing gifts during Christmas itself. Christmas trees and dinner are still popular, though. In several central European countries, gifts are given on both St. Nicholas' Day (6th December or the day before it) and at Christmas Eve (with the gifts given on St. Nick's being generally smaller, and the Christmas Eve gifts being the main ones). In Spanish-speaking countries, gifts are exchanged on the feast day of the Three Kings, which is Jan 5th.