Type sizes refer to the different sizes of typefaces used in printing and typesetting. The four type sizes mentioned are Elites (6 letters), ENS (3 letters), AGATES (6 letters), and Picas (5 letters). Elites are the largest type size, measuring 12 points, while ENS is the smallest, measuring 3 points. AGATES are slightly larger than ENS, measuring 5.5 points, and Picas are slightly smaller than Elites, measuring 10 points.