A flag is a symbol. It can represent many things, like a nation, territory, office, organization or group. Flags are simple, yet they are distinctive and meaningful. A flag should ideally be recognisable. It should not only have beauty but substance as well.

Vexillology is the scientific study of the history, symbolism, related emblems and usage of flags or, by extension, any interest in flags in general. It is concerned with research into flags of all kinds, both modern and historical, the creation of a body of practice for flag design and usage, and of a body of theory of flag development. Vexillology seeks to understand and explain the important part played by flags in the modern world.

Vexillology as a word is derived from the Latin vexillum, a term used by the Romans to refer to a kind of standard with a fabric hung from a horizontal crossbar on a pole. It is the nearest equivalent in the classical languages to what we call a flag today.

The constitution of the International Federation of Vexillological Associations (known by its French acronym, FIAV) formally defines vexillology as 'The creation and development of a body of knowledge about flags of all types, their forms and functions, and of scientific theories and principles based on that knowledge.'

Flag of International Federation of Vexillological Associations - FIAV

A person who studies flags is a vexillologist; vexillography is the art of designing flags; one who does so is a vexillographer; an admirer of flags is a vexillophile.

The vexillum was a flag-like object used as a military standard by units in the Ancient Roman army.

The word vexillum is a diminutive of the Latin word, velum, meaning a sail, which confirms the historical evidence (from coins and sculpture) that vexilla were literally "little sails" i.e. flag-like standards. In the vexillum the cloth was draped from a horizontal crossbar suspended from the staff; this is unlike most modern flags in which the 'hoist' of the cloth is attached directly to the vertical staff. The bearer of a vexillum was known as a vexillarius or vexillifer.

Vexillology or the study of flags, derives its name from this word, and a vexilloid is a standard that is not of conventional flag form.