"To form an embryo" means the process of creating the earliest stage of a developing organism, such as a human baby, plant, or animal. It is when the cells come together and start dividing to begin the growth of a new life. Full definition
Partially formed embryos float silently, bathed in amniotic fluid. (discovermagazine.com)
Most citrus trees, for example, can form embryos from the tissues surrounding the unfertilized gametes — a feat no animal can manage. (science.sciencemag.org)
We take a human embryonic stem cell, and we inject it into a monkey blastocyst [the first 130 or so cells in a newly formed embryo]. (discovermagazine.com)