A hillfort is a technical term for a kind of fortified village, constructed during the Iron Age in Europe (ca ~800-51 BC).
Hillforts were often built on natural rises, and they include a village surrounded by defensive structures, usually ditches, wooden palisades or stone walls. Although the term hillforts refers specifically to the Iron Age villages of Europe, the fortification of villages is by no means restricted to Europe or the Iron Age.
Biskupin, located on an island in the Warta River, is known as the "Polish Pompeii" because of its stunning preservation. Timber roadways, house foundations, roof fall: all of these materials were well-preserved and recreations of the village are open to visitors. Biskupin was huge, comparatively speaking, with a population estimated at 800-1000 people tucked away inside of its fortifications.
Broxmouth is a hillfort in Scotland, where evidence for deep sea fishing has been identified in an occupation dated beginning about 500 BC. The site includes numerous roundhouses and cemetery areas within and outside of several wall fortifications.
Crickley Hill is an Iron Age site in the Cotswold hills of Gloucestershire. Its earliest fortification dates to the Neolithic period, ca 3200-2500 BC. Crickley Hill's Iron Age population within the fort was between 50 and 100: and the fort had a devastating end evidenced by the archaeological recovery of hundreds of arrow points.
Danebury is an Iron Age hillfort in Nether Wallop, Hampshire, England, first built about 550 BC. It boasts terrific organic preservation for its faunal and floral remains, and studies here have provided lots of information on Iron Age agricultural practices including dairying. Danebury is justifiably famous, and not just because it is located in a place with a very silly name.
Heuneburg is more properly a Fürstensitz, or princely residence, overlooking the Danube River in southern Germany. A very old site with a long unbroken occupation, Heuneburg was first fortified in the 16th century BC, and reached its heyday circa 600 BC. Heuneburg is most famous for its princely burial, including a golden chariot, which was made up to look far costly than it actually cost to make: an example of Iron Age political spin, as it were.
Misericordia is a vitrified hillfort dated to the 5th through 2nd centuries BC. One rampart built of earth, schist and metagraywacke (silceous schist) blocks was set ablaze, making the fortification that much more substantial. Misericordia was the focus of a successful archaeological study of using archaeomagnetic dating to identify when the walls were fired.
Pekshevo is a Scythian culture hillfort located on the Voronezh River in the Middle Don basin of Russia. First built in the 8th century BC, the site includes at least 31 houses protected by ramparts and a moat.
Roquepertuse has a fascinating history that includes an Iron Age hillfort and a Celtic community and shrine, where early forms of barley beer were made. The hillfort dates to ca. 300 BC, with a fortification wall enclosing some 1300 square meters; its religious connotations including this two-headed god, a forerunner of the Roman god Janus.
Sometimes you will see hillforts that were not built during the European Iron Age referred to as "enclosed settlements". During our uneasy occupation of this planet, most cultural groups have at one time or another had to construct walls or ditches or ramparts around their villages to protect themselves from their neighbors. You can find enclosed settlements all over the world.
A vitrified fort is one that has been subjected to intense heat, whether purposeful or by accident. Firing a wall of some types of stone and earth, as you might imagine, can crystallize the minerals, making the wall that much more protected.