What is the difference between Taekwondo and Karate?

Taekwondo is a Korean martial art and the national sport of South Korea. It combines combat techniques, self-defense, sport, exercise, and in some cases meditation and philosophy.  Training generally includes a system of blocks, kicks, punches, and open-handed strikes and may also include various take-downs or sweeps, throws, and joint locks. It often incorporates self-defense techniques borrowed from other martial arts, such as hapkido and judo.  Taekwondo sparring has been an Olympic event since 2000.

Karate is a martial art developed in the Ryukyu Islands in what is now Okinawa, Japan. It was developed partially from indigenous fighting methods from Chinese kenpō. Karate is a striking art using punching, kicking, knee and elbow strikes, and open-handed techniques such as knife-hands. Grappling, locks, restraints, throws, and vital point strikes are taught in some styles.

Sources: http://en.wikipedia.org/wiki/Taekwondo, http://en.wikipedia.org/wiki/Karate