a frameshift mutation is a mutation which changes the sequence read and transcribed by the ribsome, also presenting the possibility of coding for the wrong amino acid. You can have two types; frameshift substitution or frameshift deletion. In a substitution, a mutation occurs, adding a new basepair and shift the sequence read to the right. In a deletion, a mutation deletes a base pair and moves the sequence read to the left.
frameshift substitution: CGG TAT
frameshift deletion: CTA T