give the significance of  a "lattice point".

Hi waiz,

To define repeating unit use concept of a lattice . A lattice is an infinite 1, 2, or 3–D regular arrangement of points, each of which has identical surroundings. Any periodic pattern can be described by placing lattice points at equivalent positions within each unit of the pattern.

The size of the unit cell is defined by using lattice parameters. For example the dimensions of seven crystal systems is defined by using these lattice parameters.

 

Hope this answers your question.

Cheers!