Low plasma albumin causes edema as a result of a reduction in which pressure?

Albumin makes about 75% of plasma colloid oncotic pressure in the blood which is responsible for extracting water into the circulatory system.  If albumin level is decreased, edema results.

There are many terms that relate to the same pressure, commonly used are
plasma colloid oncotic pressure, colloid osmotic pressure, oncotic pressure, or even simply osmotic pressure, depending on the term used in your course.