Wiktionary
n. A usually triangular sandwich constructed from two slices of soft crustless white bread, popular in Italy.
Wikipedia
The tramezzino is a usually triangular sandwich constructed from two slices of soft white bread with the crusts removed. Tramezzini are popular and inexpensive snack sandwiches available at many Italian bars throughout the day. Popular fillings include tuna and olive and prosciutto, but many other fillings can be used.
The origin of the tramezzino can be found in the Caffè Mulassano di Piazza Castello in Turin where it was devised in 1925 as an alternative to English tea sandwiches. Today the bar offers 40 varieties of tramezzini.
The word tramezzino was invented by Gabriele D'Annunzio as a replacement for the English word " sandwich", being easier to pronounce and a completely Italian term (albeit a neologism). "Tramezzino" sounds like "in-between", with the addition of the diminutive suffix "-ino".