In geometry, a figure is said to be chiral if it is not identical to its mirror image, or more particularly can't be mapped to its mirror images by rotations and translations alone. Such objects then come in two forms, called enantiomorphs. Chirality is equivalent to lacking a plane of symmetry (line in 2-D).
Many familiar objects are chiral - for instance, a right glove and left glove are enantiomorphic, and so are the S and Z tetrominoes of the popular video game Tetris. Some molecules are chiral, for instance optical isomers, and their study is part of stereochemistry. The fundamental laws of physics may be chiral, as the weak charge is not invariant under a reflection unless particle are replaced by their antiparticles as well, and kaon decay appears to violate even that symmetry.