I have been watching Master chef and one of the challenges that came up was trifle. I have never eaten a trifle, or really even seen a trifle in real life. What I understood from the show is that it is a dessert with fruit in it. As far as an exact composition, it is hard to get an exact recipe, and it seems to be mostly because I think the layers vary depending on what people feel like putting in it (if this is incorrect, feel free to let me know in the comments below).
What I eventually determined is that it typically starts from the bottom with a sponge cake layer at the base that can be imbibed with alcohol, usually sherry. The next layer is some sort of fruit jelly. The top two layers are then custard and whipped cream. So the overall dessert is a nice pudding. I am not sure if that is normally the way it is, but I thought it would be nice to have a gradient of sweetness: the upper cream layers being less sweet, then custard slightly more so, and the jelly most sweet (some of it soaks into the cake).
Finally, as an apple recipe, instead of the (what appears to be the standard fruit) berry jam, we go with apple jam!