A stage of the embryo’s development usually occurring around days 5-6. Initially 1 cell divides (cleaves) into 2 cells, then 4, then 8, etc. (days 1-3) before the cells compact into a morula (day 4), then a blastocyst forms (Day 5/6). Read more in my post on Embryo grading and success rates
Synonyms:
blast, blasts