The Flag of Kent is the flag

Flag

A flag is a piece of fabric with a distinctive design that is usually rectangular and used as a symbol, as a signaling device, or decoration. The term flag is also used to refer to the graphic design employed by a flag, or to its depiction in another medium.The first flags were used to assist...

 of the English

England

England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

 county of Kent

Kent

Kent is a county in southeast England, and is one of the home counties. It borders East Sussex, Surrey and Greater London and has a defined boundary with Essex in the middle of the Thames Estuary. The ceremonial county boundaries of Kent include the shire county of Kent and the unitary borough of...

. It features the white horse of Kent

White horse of Kent

The White horse of Kent, or the White Horse Rampant, is a symbol of Kent, a county in South East England.The figure of the prancing white horse can also be referred to as Invicta, which is the motto of Kent.-Origin:...

 on a red background, a theme used in several other Kent related coats of arms and logos or symbols. It is sometimes referred to as the Invicta Flag or Invicta Flag of Kent, after the motto of Kent, Invicta

Invicta (motto)

Invicta was used in Roma invicta meaning "Unconquered Rome" and is the motto of the county of Kent, England.-Theories of origin:...

.

The Flag Institute

Flag Institute

The Flag Institute is a research and documentation centre for flags and flag information, founded on St George's Day, 23 April 1971 by William Crampton and Captain EMC Barraclough CBE RN. Although not an official body, it is the principal advisor and designer of flags to the government of the...

 note, in the flag's entry on the UK Flags Register that:

This is the traditional flag of Kent, supposedly based on that of Horsa, the Jute. Horsa was the brother of Hengest

Hengest

Hengist and Horsa are figures of Anglo-Saxon, and subsequently British, legend, which records the two as the Germanic brothers who led the Angle, Saxon, and Jutish armies that conquered the first territories of Great Britain in the 5th century AD...

, who founded the Kingdom of Kent in 449. The first recorded reference is in 1605.

The flag is an adaptation of the traditional arms of Kent to which the quote refers. These arms were attributed anachronistically to the Kingdom of Kent

Kingdom of Kent

The Kingdom of Kent was a Jutish colony and later independent kingdom in what is now south east England. It was founded at an unknown date in the 5th century by Jutes, members of a Germanic people from continental Europe, some of whom settled in Britain after the withdrawal of the Romans...

, but used by the Justices of Kent for many years. The arms were officially granted to Kent County Council

Kent County Council

Kent County Council is the county council that governs the majority of the county of Kent in England. It provides the upper tier of local government, below which are 12 district councils, and around 300 town and parish councils. The county council has 84 elected councillors...

on 17 October 1933 (and re-confirmed to its successor in 1975). The flag was accepted by the Flag Institute as that of the historic county on the basis of its traditional use.