Vexillology; the study of flags.

The flag is the embodiment, not of sentiment, but of history. Woodrow Wilson was speaking of the U.S. flag when he made that statement in an address in June of 1915, but those who engage in vexillology - that is, vexillologists - would likely find the comment applicable to any national banner. Vexillologists undertake scholarly investigations of flags, producing papers with titles such as "A Review of the Changing Proportions of Rectangular Flags since Medieval Times, and Some Suggestions for the Future." In the late 1950s, they coined vexillology as a name for their field of research from vexillum, the Latin term for a square flag or banner of the ancient Roman cavalry. The adjectives vexillologic and vexillological and the noun vexillologist followed soon thereafter.

Merriam-Webster. (n.d.). Vexillology. In dictionary. Retrieved April 12, 2021, from

Down below a index of country flags.

Credit for the images goes to Flagpedia & Wikimedia