The BLT (bacon, lettuce, and tomato) is a type of bacon sandwich. The BLT traditionally has several strips of well-cooked or even crispy bacon, leaves of lettuce (traditionally iceberg or romaine), and slices of tomato, between slices of bread (commonly toasted). Mayonnaise is the traditional condiment for the BLT. The BLT is regarded as being the second most popular sandwich in the United States, after the ham sandwich.
BLT sandwiches are believed to have descended from late Victorian era tea sandwiches. Between 1930 and 1950, cookbooks typically listed cheese as an ingredient.
The BLT became popular after World War II because of the rapid expansion of supermarkets that allowed for ingredients to be available year-round. The initials, representing "bacon, lettuce, tomato", likely began in the American restaurant industry as shorthand for the sandwich.