A hedgehog is any of the spiny mammals of the subfamily Erinaceinae and the order Erinaceomorpha. There are 17 species of hedgehog in five genera, found through parts of Europe, Asia, Africa, and New Zealand (by introduction). There are no hedgehogs native to Australia, and no living species native to the Americas (although fossils of at least four extinct species were discovered in South America). Hedgehogs share distant ancestry with shrews (order Soricidae), with gymnures possibly being the intermediate link, and have changed little over the last 15 million years. Like many of the first mammals they have adapted to a nocturnal, insectivorous way of life.
The name 'hedgehog' came into use around the year 1450, derived from the Middle English 'heyghoge', from 'heyg', 'hegge' = hedge, because it frequents hedgerows, and 'hoge', 'hogge' = hog, from its piglike snout. Other names include 'urchin', 'hedgepig' and 'furze-pig'.
The purchase of domesticated hedgehogs has seen a considerable increase in the last few years, owing to their apparently innocent and playful looks. Hedgehogs are considered a low-maintenance pet. Their curiosity and need for stimuli make for quick adjustment to their owners, and their eating and waste habits make for a relatively clean housing environment for the pet. Overall they exhibit very few vulnerabilities to species-specific disease (although several do exist) and are easy to care for.
Source: Wikipedia, "Hedgehog", available under the CC-BY-SA License.