A gene is a hereditary unit with a specific location on a chromosome. It determines a characteristic in an organism by specific proteins and can replicate during cell division.
An allele is one of two or more forms of a gene at corresponding loci on homologous chromosomes. A person usually has two alleles for each gene - one from each parent. If both alleles are the same, the person is homozygous. If the alleles are different, the individual is heterozygous and the dominant allele will prevail or be expressed.
So what is the difference in simple terms? Genes are part of your DNA. Alleles are different versions of the same gene. They occur in pairs and can be dominant or recessive. Alleles determine which version of the gene will be expressed in an individual. This creates the remarkable uniqueness we each have!