Perigord Black Truffle (Tuber Melanosporum), or, French Black Truffle is the most common of Truffles. Actually, there are quite a number of Truffle species. A Truffle is a fungal fruiting body that develops underground and relies on mycophagy for spore dispersal. Almost all truffles are ectomycorrhizal and are therefore usually found in close association with trees.
The Black Truffles (or Perigord Truffle) are highly prized as a food. Brillat-Savarin called these truffles "the diamond of the kitchen". Edible truffles are held in high esteem in French, northern Italian and Istrian cooking, as well as in international haute cuisine.
Check out wikipedia for more info. Stav has some blog posts on fresh truffle as well, click here to go to the blogs and type "Truffle" into the search field.