Tiramisu is an Italian layered desert consisting of Savoiardi cookies (biscuits to the British, or "lady fingers" colloquially—slightly dry small sponge cake wafers) dipped (or soaked but not to saturation) in very strong coffee (espresso, traditionally) then layered with a very light custard made of Zabiglione (egg yolks, sugar and sweet wine (traditionally Marsala) or a liquor as a flavoring) and Mascarpone (a very rich, slightly sweet and slightly stiff Italian cream cheese). The carefully dipped-in-expresso cookies are then layered with the custard, then sprinkled with cocoa, and refrigerated.
The word tirami-su quite literally means "pick me up"; this makes sense if you think about the effects of the coffee, and the liquor. I'm not even going to attempt to unravel the history of Tiramisu as a dessert though; it's far too complicated, and too likely to cause headaches; I'd much rather eat it. I will note the following: