Information-theoretic security
Information-theoretic security is a cryptosystem


Nitpick: information-theoretic security is a property that a cryptosystem can have against a particular attack model. AES is a cryptosystem, but doesn't have this property against any of the usual models; the one-time pad is a cryptosystem that does against passive attackers (but not active ones).

Other systems that have information-theoretic security, off the top of my head:


The one-time pad, against passive attackers.
Pedersen commitments, against the opener (but not against the committer).
ElGamal encryption used as a commitment, against the committer (but not the opener).
A bunch of OT systems of the Chu-Tzeng style, against either the sender or the recevier (against both at once is impossible - same goes for commitments).


Some of the above schemes are very much commercially used. 

QKD is a very specific form of quantum cryptography, the two terms are not equivalent.