There are lots of words and terms to do with castles that are not widely used by everyone, so here's a handy guide to understanding what's going on........
Bailey A courtyard
Barbican An outwork that protects a gate
Buttress Stone support built against a wall to reinforce it
Castle A fortified, usually walled residence, as of a prince or noble in feudaltimes.
Crenel The open section of a battlement
Crenellation Battlement
Curtain A length of wall surrounding a castle enclosure
Dinas in Old and Middle Welsh it is a masculine noun meaning "fort or citadel", often applied to hillforts.
Donjon A great tower or keep, but can also mean an upper Bailey or lord's private area
Hillfort Large enclosures on the top of hills surrounded by one or more earthworks Usually the ramparts also have a ditch running alongside them. They usually contain the remains of round houses and other buildings. Although they may have their origin in the
Bronze Age (2300BC to 800BC) or even earlier they were most commonly built in the Iron Age (800BC to AD43). They may have continued to be used into the Roman period.
Keep The word used in England from the 16th century to describe the donjon or great tower
Moat A ditch, either wet or dry
Motte An earth mound
Murder Hole a section between the main gate and a inner portcullis where arrows, rocks, and hot oil could be dropped from the roof though holes
Parapet The outer wall of a wall walk
Portcullis A lattice made of wood clad in iron, or occasionally iron alone, dropped to block a gate
Postern A small rear door
Putlog/Putlock Holes small holes in the walls of structures to receive the ends of poles (small round logs) or beams, called putlogs or putlocks, to form scaffolding. Putlog holes may extend through a wall to provide staging on both sides of the wall.
Rampart An earthern bank
Ring-work A circular or oval earthwork with bank and ditch
Turret A small tower
Wall walk A passage along the top of a wall
Wing-wall A wall descending the slope of a motte