I always wondered about this and now I know:

I was asked by a personal friend with two children through IVF, if her children are genetic matches for each other. Her youngest child was born from a frozen embryo, which was created from an egg (“oocyte”) obtained from the same oocyte collection as her eldest child. “Does this mean they are twins?” she asked me.

This is a really interesting question, as the children would indeed be called twins if they had been born together, rather than one embryo having been frozen. However, in this case they would have been fraternal twins, not identical. Fraternal twins are only called twins because they gestate together inside the uterus and are born at the same time. They are not a genetic match for each other as they did not split from the same embryo. A single embryo which splits into two separate embryos results in both embryos having the same DNA as each other and are therefore termed “identical”.