Implantation is the attachment of blastocyst to the uterine wall (endometrium). It occurs after 6-7 days of fertilization. During implantation, the trophoectoderm (trophoblast) comes in contact with the endometrium of the uterus and sinks into a pit formed in the endometrium and get completely burried in the endometrium. Trophoblast cells form specialized structures called villi, which help in absorption of nutrient materials.