Knight (in form of title sir or sire) is a person granted an honorary title of knighthood by a monarch or other political leader for service to the Monarch or country, especially in a military capacity. Since humanity of Northern Kingdoms and Nilfgaard strongly resembles Medieval Europe, there are many knights in the witcher world.
Knights also form army units and regiments in some states. For example, in Redania they are grouped into cavalry while in Temeria they prioritize fighting by foot. And then there is Toussaint, a land of love and wine within the Nilfgaardian Empire, that does not have an army and so relies on noble knights errant and the Ducal Guard.
Knights who choose not to stay with their ruler may become a knight for hire, mercenaries with a noble title, or they may join a knightly order such as the Order of the Flaming Rose.
Most knights are males, but there are some exceptions, such as the knight Alondra.
For a complete list, see Category:Knights.