Krypton is a fictional planet in Lois and Clark: The New Adventures of Superman.
It was Superman's home planet which was destroyed after a terrible virus that spread to it's core affected it.
Superman was sent to Earth as a baby before the planet exploded while others escaped and formed a new civilisation on a new Krypton.
It had a red sun as opposed to the yellow sun of Earth which made the Kryptonians just as ordinary as humans.
When the planet exploded, fragments of the planet scattered on Earth forming rocks known as Kryptonite which was extremely deadly to all Kryptonians.