Large format is basically a term for the largest types of negatives and positives. When scanned, large format film can provide some of the highest resolution images you can get! In fact, a 4×5 image has about 16 times the area (and resolution) of a standard 35mm frame. The most common large format size today is the 4×5 format, which was common in cameras used in the 1930s-1950s.
Large format refers to any imaging format of 4×5 inches (102×127 mm) or larger. Large format is larger than the more commonly found “medium format”, the 6×6 cm (2¼×2¼ inch) or 6×9 cm (2¼×3½ inch) size of Hasselblad, Rollei, Kowa, Pentax etc. cameras (using 120 and 220 roll film), and much larger than the 24×36 mm (~ 1.0 x 1.5 inch) frame of 35 mm format.
Use the chart below as a comparison between large format sizes, and the standard sizes.