Multiple alleles refers to an inheritance pattern where a series of 3 or more alternative forms of a gene are possible, however in a normal diploid individual only 2 can exist (one from the father and one from the mother). An excellent example of this is blood type. Multiple alleles gives us the possibility of 6 different blood types.
Quick translate "x is 12 units from 20" into an equation. what are the values of x being described? if you can answer any of my other questions that'd be great too