They are genes that are found near each other on the same chromosome. If genes on separate chromosomes, are never linked . Each gamete gets a single copy, determined at random, of each chromosome. Because there is nothing holding them together, the alleles can pass to gametes in any combination.
Multiple Genes
It's known as a poly gene. In other words it's a group consisting of different gene responsible for a particular trait. To go more in depth it a group of non-epistatic genes that influence a phenotype trait.