Final answer:
A crystal is a body bounded by planar surfaces arranged in a definite plane. The internal arrangements of the atoms are represented by the crystal lattice.
Step-by-step explanation:
A body bounded by planar surfaces arranged in a definite plane is called a crystal. Crystals are substances in which the particles are arranged in an orderly, repeating, three-dimensional pattern known as a crystal lattice. The crystal lattice represents the internal arrangements of the atoms in the body, showing how they are bonded to one another and the approximate arrangement of atoms in space.