Feudal aid was a financial duty in which vassals would be ready to assist their lord monetarily such as in giving ransom money in time of need. This was a practice that was widespread in Europe (such as England, France, and Germany) during the Middle Ages.
A standing army is a group of soldiers ready to do battle. This army is permanent (even in times of peace), always ready to fight and the soldiers are often professional trained. This is contrary to a reserve or temporary army, which is only active during a war and is disbanded when the threat of war is over.
King John (24 December 1166 - 19 October 1216) ruled England in the 1200's, from 1199 until his death in 1216 to be precise.
A homage was a ceremony where men become vassals in a lord's manor. It was a medieval oath of allegiance in which a feudal vassal pledged reverence and submission to his feudal lord.
Knights were able-bodied men who are hired by the vassal for the protection of the lord. In Europe, knights were mostly mounted warriors. Most of the knights descended from some kind of nobility because the equipment (like an armor and a horse) were very expensive.
