A squire is a young boy or girl attendant to a knight or other noble who are part of the nation's military. Well looked after, with food, clothing and lodgings, in return for faithful service they are trained to fight, eventually becoming part of the knight's banner or an officer in the military.
Most officers will have spent some time as a square, even nobles spend time as a squire, some for the parent, some for older siblings. Time spent as a squire hones skill, determination and honour.