This is a random error/change in the dna sequence. these may be inherited or occur in cells during the lifetime of the organism.

This is the definition of a DNA mutation.

Depending on which part of the genome is affected, the consequences of a mutation may vary. A mutation is said to be hereditary if the mutated genetic sequence is transmitted to the next generation (see germinal mutations). It is one of the elements of biodiversity and one of the many factors that may be involved in the evolution of the species.