blastocyst
US /ˈblæs.tə.sɪst/
UK /ˈblæs.tə.sɪst/
1.
blastokista
a blastula (= the early stage of development, consisting of a layer of cells around an empty space) of the embryo of a mammal:
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Five to six days after an egg is fertilized by a sperm, a tiny ball of cells develops called a blastocyst.