Aestivate - Means to pass the summer in a certain manner or condition, often in a dormant or torpid state. As many tortoises are desert or semi-desert animals, some species can go into a state of torpor or hibernation in response to very dry conditions or hot temperatures.

Bone Density Ratio - A method of working out whether a tortoise has the correct weight to height ration to allow it to hibernate (see hibernation page for full details).

Carapace - The shell of a tortoise or turtle. Often applied to the upper shell only.

Chelonian - A collective term meaning any turtle and tortoises. Scientifically, all turtles, tortoises, and terrapins belong to the order 'chelonia'.

CITES - Stands for 'The Convention on International Trade in Endangered Species'. Sets world wide standards and restrictions on the trade in certain animals, plants, and products derived from them.

Cloaca - The vent or common opening (bottom) in tortoises and turtles through which the intestinal, urinary, and reproductive tracts empty.

DEFRA - The Department for Environment, Food and Rural Affairs. Responsible for monitoring the trade in endangered chelonians in the UK.

Hibernate - Hibernation is to be inactive through the winter in a state of reduced metabolic activity. Many tortoises and turtles hibernate as the weather becomes colder. Those tortoises from warmer climes often do not hibernate at all. in the UK.

Jackson Ratio - The Jackson ratio is a method of assessing whether a Mediterranean tortoise has the correct weight to height ration to allow it to hibernate (see hibernation page for full details).

Plastron - The lower half of a tortoises shell. Plastron length is how tortoises are usually measured.

Poikilothermic - Meaning 'cold blooded'. All reptiles including tortoises and turtles are poikilothermic and rely on the sun and the environment to maintain their body temperature.

Reptile - Any cold-blooded vertebrate of the class Reptilia which includes tortoises, turtles, snakes, lizards, alligators and crocodiles.

Scute - The plates which cover the upper portion of the shell. The name for an individual section of a tortoises shell. Each part of the upper shell or carapace is a 'scute'.

Temperature gradient - A temperature gradient is a result of different parts of an area/habitat/enclosure being maintained at different temperatures in order to provide a gradient (slope) of temperature from hotter to cooler. This allows tortoises and turtles to regulate their own body temperatures.

Terrapin - Any chelonian which lives in freshwater for all or part of the time.

Tortoise - Any chelonian which lives solely on land.

Tortoise Table - An indoor enclosure for tortoises (often made of wood) with an open top and low walls to provide adequate ventilation and allowing correct heating/lighting etc.

Turtle - Any sea dwelling/marine chelonian. This is a mostly European definition of the word. In America all chelonians are called turtles regardless of where they live.