A Monozygote refers to an Identical Twin. It is one of the two identical organisms developed from a single egg that has split. In the rare instance that more than two are formed from the one egg, then each of them from that egg would be a monozygote (e.g., identical triplets). Monomeans one, or single Zygote refers to the organism(s) that develop from the cell that forms as soon as an egg is fertilized.
Mirror Twins are always monozygote twins. This does not mean that fraternal twins won't be a righty and a lefty - if your family tends to run left handed.
Codominance is when a pair of nonidentical alleles at a gene locus both affect the phenotype in heterozygotes, and therefore both alleles are expressed simultaneously. This results in the expression of a unique phenotype that is a combination of the traits associated with each allele.
It means "from a different egg". It is generally used to describe non-identical twins who formed embryos from 2 or more different egg cells. Identical twins are called monozygote as they separated from the same fertilized egg cell.