Allele

 The variant of nucleotide sequence of a DNA is called allele. 

Allele differs from each other in a single position nucleotide polymorphism. But it also can differ in thousand of base pair deletion and insertion.

Most of the allele differs among them in a results as phenotype change,  but not in gene coding.  For example, white and purple colour of pea plant flower is results of different allele,  but not in gene difference.