Is
a non-mendelian inheritance pattern that involves more than 2 alleles. For example of multiple allele there are the ABO blood group system and leaves of the Morning Glory Flower.
Taking the example of the morning glory. There are 3 multiple alleles for a regular leaf
A , tatsutada leaf
a and willow-leaf
a´ arrowhead to leaf of the morning glory. So they are multiple allele. Incidentally, they are dominance
A,
a,
a´ in that order.