A permanent, heritable change in the nucleotide sequence in a gene or a chromosome. In genetics, mutation may be a small scale or large scale. It may arise from faulty deletions, Insertions or exchange of nucleotide in genetics material as caused by exposure to UV rays, viruses etc. Such change may result in new character or trait.
Mutation is a natural process that changes a DNA sequence. As a cell copies its DNA before dividing, a 'typo' occurs every 100,000 or so nucleotides.

 We can take the example of human species. The whole human family is of one species with the same genes. Mutation creates slightly differently versions of the same genes, called alleles. These small differences in  DNA sequence make every individual unique.