: a placenta made up of villi diffusely scattered over almost the whole surface of the chorion (as in whales, swine, and horses)

What do you mean by diffuse?

: to spread out : to move freely throughout a large area. : to exist or be known throughout an area. : to cause (light) to be soft and spread out.

What are the abnormalities of placenta?

These placental disorders are called placenta previa, placenta accreta, placenta increta or placenta percreta. Placental disorders are usually diagnosed by ultrasound in the second trimester (about 18 to 20 weeks into a pregnancy). Placenta previa occurs when the placenta covers some or all of the cervix.