The Basilisk is a legendary serpent closely related to the Cockatrice and believed to be inspired by varied snake species found in the world. It was considered a "king" of the serpents and had the frightening ability to kill with a single glance, known as petrification.
The Basilisk is also said to be so incredibly poisonous and deadly that it leaves behind a burning trail of venom everywhere it goes, and indeed, this is how one could identity a Basilisk's hole, due to the ground being scorched around it.
The only way folklore said that the Basilisk could be harmed or driven away was via the odor of a weasel, presumably due to the fact weasels are natural predators of lizards and snakes (especially the mongoose).
The word "Basilisk" in science refers to Basiliscus, a South American genus of lizard containing four species.