The ABO gene is said to have multiple alleles state what this means

Multiple alleles means that there are three or more forms of a gene for a trait. That doesn't mean that a person can have all three of them. The person still only gets two ... it's just that there are three or more of the alleles in the gene pool that are available.

I tell my students that it's like having three trays of cookies, each tray having a different kind of cookie. Your instructions are that you may have any two cookies that you want. Can you have two from the same tray? Yes. Can you have two different kinds? Yes, you can have one of one kind and one of a second kind. Can you have one from each of the three trays? No, you can only have two cookies.

That's how multiple alleles work. Blood type is controlled by multiple alleles: A, B, and O. Can a person have AA? Yes. Can a person have OO? Yes. Can a person have AB? Yes. Can a person have BO? Yes (but it makes everybody laugh). Can a person have ABO? No, only two alleles and no more.

So the answer is ... No, a person does not have more than two alleles for a single gene.

Of course there are exceptions, but not normal exceptions. Only abnormal exceptions that happen when a person has an unusual number of chromosomes. If you are just learning genetics, you don't have to worry about these exceptions yet.

Multiple alleles - a type of non-Mendelian inheritance pattern, involves more than just the typical two alleles that most of the time code for a certain characteristic in a species. With multiple alleles, that means there is over two phenotypes available depending on the dominant or recessive alleles that are available in the trait and the dominance pattern the individual alleles follow when combined together.