Arrow loops were narrow openings or crosses in the castle walls that enabled soldiers to safely launch arrows at attackers outside. The walls behind an arrow loop were often cut away at an angle so that the archer had a wide range of view and room to fire. These cut-away areas were known as embrasures. 

Baileys

The castle baileys were large areas of flat land or courtyards in which the castle was built around. Much of the labor and activity of the castle occurred in the baileys. The workshops, stables, chapel and livestock were usually located here.  Castle farmers and laborers sometimes lived in the bailies. Some castles had a single bailey, while others had multiple baileys. Sometimes, new baileys were constructed when the castle expanded.

Battlements, common features of castle and city ramparts, are openings cut at intervals at the top of the ramparts or walls to allow for archers and defenders to shoot arrows and discharge other weapons. The solid areas in between the battlements are called merlons. A wall with battlements is said to be crenellated.

The Chapel was an important part of life in the castle and the primary location for community gatherings and prayer. Some castles had multiple chapels, while others had only one.  Most castle chapels were beautifully decorated with sculptures, murals, and stained glass and the ceilings were often vaulted. Some chapels even had crypts.

The Curtain Walls were the main defensive walls of the castle that protected the inner bailies.  The walls were called "curtain walls" because they actually consisted of several walls connected like a curtain draped between two towers. Early curtain walls were made of wood and referred to as palisades.  Such walls were prone to decay and fire and were replaced by stone walls in the late 11th century.  Curtain walls were normally about 30 feet high and between 3 and 20 feet thick! 

The drawbridge was the protective entrance to the castle that spanned the width of the castle moat, from the barbican to the gatehouse. When the drawbridge was closed,  the entrance to the castle was sealed.  It was almost always made of wood and later versions had ropes and pulleys that enabled castle defenders to lift the drawbridge easily.  Lifting gaffes or arms were sometimes added to drawbridges to make them easier to lift.

The castle gatehouse was strategically the most important part of the castle, as the castle entrance was always the most vulnerable part.  The gatehouse was usually heavily fortified and equipped with a drawbridge and portcullis, a metal or iron-bound wooden grating that would slide down in front of the entrance. In later castles, the gatehouse was the most elaborate part.

The Keep was a large, fortified structure in which defenders could retreat to as a last resort during an attack. It is sometimes referred to as the donjon or great tower.  The basements of some castle keeps had prisons, which is how the word "dungeon" evolved.  Some keeps were supported and strengthened by buttresses and the walls were unusually thick (up to 15 feet!)   Keeps in later
castles served many purposes besides defense and sometimes included the lord's private residence. 

Living Quarters

The Main Tower is the largest of the castle towers and was usually the central lookout located on the corner of the curtain wall.  It provided additional protection and stability for the castle. Some towers were also equipped to hold prisoners. The main tower of the Tower of London was known to hold political prisoners.

The moat was a water filled ditch that surrounded the castle. Like the majority of castle features, it provided defense against a direct assault against the castle and created a difficult barrier for soldiers and horsemen. Moats could be 30 feet deep and 30 feet wide. To fill the moat, water was diverted from a nearby stream or river. Some moats were filled with wooden stakes instead of water.

The open gorge tower was one of three kinds of towers commonly found in medieval castles. It was a combination of an open and closed tower, as it was closed to the level of the wall-walk, where it opened up into a balcony that could be patrolled.  These towers were particularly common in ramparts that enclosed cities.

Ramparts are protective or enclosing walls designed as a defense against attacks. Ramparts usually refer to walls that enclose and entire city or settlement, but the outer castle walls are sometimes called ramparts as well. These walls are also sometimes included in the description of the curtain walls.

The Castle stables were used to house horses and livestock and were usually located in one of the lower baileys. Some castles had stables especially for hunting dogs.