Definition - What does Frostie mean?
A frostie is a slang term for a frozen embryo.
FertilitySmarts explains Frostie
In vitro fertilization (IVF) can include either a fresh embryo transfer or a frozen embryo transfer (FET). Embryos from a fresh IVF cycle can be frozen, or cryopreserved for future use. This is achieved through rapid freezing known as vitrification that does not harm the embryos.
The term frostie is used most frequently in online fertility message boards.