The design and description of flags typically uses specialised flag terminology with precise and technical meanings, and is hence a form of jargon.
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Flag illustrations generally depict flags flying from the observer's point of view from left to right, the view known as the obverse (or "front"); the other side is the reverse (or "back"). There are some exceptions, notably some Islamic flags inscribed in Arabic, for which the obverse is defined as the side with the hoist to the observer's right.
A vexillological symbol is used by vexillologists to indicate certain characteristics of national flags, such as where they are used, who uses them, and what they look like. The set of symbols described in this article are known as international flag identification symbols, which were devised by Whitney Smith.
Some countries use a single flag design to serve as the national flag in all contexts of use; others use multiple flags that serve as the national flag, depending on context (who is flying the national flag and where). The six basic contexts of use (and potential variants of a national flag) are:
civil flag – Flown by citizens on land.
state flag – Flown on public buildings.
war flag – Flown on military buildings.
civil ensign – Flown on private vessels (fishing craft, cruise ships, yachts, etc).
state ensign – Flown on unarmed government vessels.
war ensign – Flown on warships.In practice, a single design may be associated with multiple such usages; for example, a single design may serve a dual role as 
war flag and ensign. Even with such combinations, this framework is not complete: some countries define designs for usage contexts not expressible in this scheme (such as air force ensigns, distinct from war flags or war ensigns, flown as the national flag at air bases; for example, see Royal Air Force Ensign).
Other symbols are used to describe how a flag looks, such as whether it has a different design on each side, or if it is hung vertically, etc. These are the symbols in general use:
Normal or de jure version of flag, or obverse side
Design was proposed in the past, but never officially adopted
Design is a reconstruction, based on past observations
Reverse side of flag
Design is an acceptable variant
Alternative version of flag
De facto version of flag
Flag has different designs on its obverse side and its reverse side
Obverse side meant to be hoisted with pole to the observer's right
Design officially authorized to represent nation by government of that nation
Design used in the past, but now abandoned (this symbol is not part of Smith's original set)
Reverse side is mirror image of obverse side
Reverse side is congruent to obverse side
Information on reverse side is not available
Flag can be hung vertically by hoisting on a normal pole, then turning the pole ninety degrees
Flag can be hung vertically by rotating the design first
Vertical hoist method of flag is unknown
Design has no element which can be rotated
Flag can only be hoisted vertically