Planar density is defined as effective number of atom on a crystal plane divided by the area of that plane. It is one of the characteristics of different crystal systems like SC, FCC, BCC, HCP.
It is used to find the slip plane.
Similar to planar density there is a term called as linear density where we find effective number of atoms per unit length.
Through this video you can understand different planes with planar density values and their unit.
