What is meant by the term chiral?

Chirality is defined rather grandly as asymmetry such that an image and it's reflection are not superimposable. This means that if you reflect the object in a mirror it won't look exactly the same.

For example, a star is not chiral, because if you reflect it, you would be able to put the reflected image on top of the original. On the other hand, your hands are chiral - they are reflections of each other, but you can't put one on top of the other - think of it as trying to put a glove for your left hand on your right hand.