Yeomanry is a designation used by a number of units or sub-units of the British Territorial Army, descended from volunteer cavalry

Cavalry

Cavalry or horsemen were soldiers or warriors who fought mounted on horseback. Cavalry were historically the third oldest and the most mobile of the combat arms...

 regiments. Today, Yeomanry units may serve in a variety of different military roles.
In the 1790s, the threat of invasion of the Kingdom of Great Britain

Kingdom of Great Britain

The former Kingdom of Great Britain, sometimes described as the 'United Kingdom of Great Britain', That the Two Kingdoms of Scotland and England, shall upon the 1st May next ensuing the date hereof, and forever after, be United into One Kingdom by the Name of GREAT BRITAIN. was a sovereign...

 was high, after the French Revolution

French Revolution

The French Revolution , sometimes distinguished as the 'Great French Revolution' , was a period of radical social and political upheaval in France and Europe. The absolute monarchy that had ruled France for centuries collapsed in three years...

 and the rise of Napoleon Bonaparte. To improve the country's defences, volunteer regiments were raised in many counties from yeomen

Yeoman

Yeoman refers chiefly to a free man owning his own farm, especially from the Elizabethan era to the 17th century. Work requiring a great deal of effort or labor, such as would be done by a yeoman farmer, came to be described as "yeoman's work"...

.