Terms that refer to the most common molecular arrangements in
liquid crystals.
Nematic refers to a random arrangement of molecules. The molecules are arranged in layers, but the ends of molecules don't always coincide. The top of one molecule doesn't necessarily coincide with the top of another molecule. Nematic is the arrangement of typical liquid crystals in watches and alarm clocks.
Smectic refers to an orderly arrangement of molecules. These molecules are in layers, and the tops and bottoms of each molecule coincide with the tops and bottoms of every other molecule.
While both arrangements allow molecules to rotate about their long axes, neither allows the molecules to rotate end over end. They spin around and move about one another, but never flip over.