Knight

[Sarah]

Rank in the fuedal system, one below baron and one above the general peasants.
Developed during the 800s in a kingdom covering France and a lot of the surrounding area, and rapidly spread to the rest of Europe as far east as Russia and as far south as Spain and Italy. Kings were finding they owned more land than they could control, so they gave vast expanses of it to barons (dukes, counts, etc) in return the barons would pay taxes to the king and would fight for him when it was demanded of them, and they must provide an agreed number of men. Barons are like the medieval equivilant of generals.
The barons continued to break up this land into smaller patches, which was controlled by a knight. The knight usually owned one or two villages in his land. The knight would tax the peasants in his land. In return for this, the knight must fight for their lord baron when called upon, and also pay taxes to him, exactly the same duties that the king expects from the barons.
The knight could be viewed as the medieval equivilant of captains/minor officers today. They recruited both men-at-arms (peasants aspiring to be honourable warriors) and archers (peasants that played the less honourable role of using bows/crossbows to fight,) and took these men with them when the baron called them to fight.
The knight is a trained killer. Taken from a family of high rank, the young knight (or page) left home at about the age of 6 to live with another knight, or even a baron, in their manor or castle. For the first 4 or so years, they were taught manners, such as how to speak different languages or how to carve a roast. From the age of around 10, they were upgraded into squires: knights to be. Training as a squire was particulry difficult. By about the age of 18, the knight was a fully trained and honed killer, and was knighted by their master in a long knighting ceremony.
Knights from around 1100AD onwards were expected to follow a code of chivalry, which meant being polite to everyone and being generous to the poor. Knights are sometimes dramatised; many knights ignored the code and were simply ruthless, greedy killers. Most base rules were followed however: it was considered cowardly to use a bow, and it was also very dishonourable (and also a waste of ransom money) to kill a defenceless or surrendering opponent.
Contrary to popular belief, knights were NOT common soldiers in armour. Knights were men of rank, and it was rare to see huge armies of knights without a vast number of peasant infantry accompanying them. Sometimes the knights and men-at-arms would gather to lead the first wave, as it was their honour and right to do so, but as tactics became more and more important in medieval warfare this custom was less common.

[Sarah]

1 A medieval tenant giving military service as a mounted man-at-arms to a feudal landholder.

2 A medieval gentleman-soldier, usually high-born, raised by a sovereign to privileged military status after training as a page and squire.

3 A man holding a nonhereditary title conferred by a sovereign in recognition of personal merit or service to the country.

4 A man belonging to an order or brotherhood.

5 A defender, champion, or zealous upholder of a cause or principle.

6 The devoted champion of a lady.

7 A chess piece, usually in the shape of a horse's head, that can be moved two squares along a rank and one along a file or two squares along a file and one along a rank. The knight is the only piece that can jump other pieces to land on an open square.

[Renato]

(in the Middle Ages) a man who served his sovereign or lord as a mounted soldier in armour.

[ThomasSlege]

a chessman shaped to resemble the head of a horse; can move two squares horizontally and one vertically (or vice versa)