Big Three
In quizbowl parlance, the Big Three are the categories of literature, science, and history. The Big Three are so named because they each take up a comparatively large share of the distribution (and take up a majority of most packets when taken together), and are therefore viewed as particularly important categories to the game.
In ACF and mACF tournaments, the Big Three each take up at least 4/4 tossups/bonuses out of a 20/20 packet (so each one takes up about 20 percent of the questions in a packet) and together they make up 60% of any given packet. The amount of any individual Big Three category is very rarely reduced or increased without changing the other two, because of the resulting imbalances for specialists in each category (with potential for skewed results and the like). NAQT's percentages are similar, though there is slightly more science than literature or history, and the proportions vary slightly from packet to packet.