Definition of Frameshift Mutation
A frameshift mutation is a type of mutation in which the addition and deletion of a nucleotide are involved but the number of base pairs that are deleted should not be divisible by three. This divisible by three is very important as the cells have the ability to read a gene in the form of groups that are formed by three bases.
Each group having three bases in it corresponds to any of the twenty amino acids that are used in building up a protein molecule. If a mutation damages and disrupts this reading frame and eventually a wrong amino acid is being put up in that place, then the whole sequence of DNA will be read in a wrong way.