Gene amplification is a term used to describe a host of processes that occur at to produce gene products which are needed in large quantities. The term is a bit slippery. It has not been normalized in its usage in molecular biology, and you may even run into it used to describe the process of PCR (polymerase chain reaction. In living organisms, you may see 'gene amplification' used to describe the elaboration of 'extrachromosomal' DNA for the transcription of a large number of RNAs, such as within the nucleolar region of an oocyte where a large number of extra copies of rRNA genes to be temporarily created, allows the oocyte to manufacture a huge number of ribosomes as the egg matures. Gene amplification is also used to describe tandem gene duplications in the localized structures within the genome called 'tandem repeats'.