Source: National Institutes of Health

Adult stem cell

An undifferentiated cell found in a differentiated tissue that can renew itself and (with certain limitations) differentiate to yield all the specialized cell types of the tissue from which it originated.

Blastocyst

A preimplantation embryo of about 150 cells. The blastocyst consists of a sphere made up of an outer layer of cells (the trophectoderm), a fluid-filled cavity (the blastocoel), and a cluster of cells on the interior (the inner cell mass).

Differentiation

The process whereby an unspecialized early embryonic cell acquires the features of a specialized cell such as a heart, liver, or muscle cell.

Embryonic stem cells

Primitive (undifferentiated) cells from the embryo that have the potential to become a wide variety of specialized cell types.

Embryonic stem cell line

Embryonic stem cells that have been cultured under in vitro conditions that allow proliferation without differentiation for months to years.

Inner cell mass

The cluster of cells inside the blastocyst. These cells give rise to the embryonic disk of the later embryo and, ultimately, the fetus.

Long-term self-renewal

The ability of stem cells to renew themselves by dividing into the same non-specialized cell type over long periods (many months to years) depending on the specific type of stem cell.

Plasticity

The ability of stem cells from one adult tissue to generate the differentiated cell types of another tissue.

Pluripotent

Ability of a single stem cell to develop into many different cell types of the body.

Somatic stem cells

Another name for adult stem cells.

• More Terminology: National Institutes of Health