The sixth letter of the Greek alphabet (Ζ, ζ) corresponding to English z.

In ancient Greek, it was pronounced as zd or dz and in modern Greek as z.

1. A potential gradient that arises across the interface between the boundary liquid layer in contact with a solid and the movable diffuse layer in the body of the liquid.
2. Electrokinetic potential refers to the potential developed across any interface separating two phases as a result of the accumulation of electrons in one phase and the loss of electrons in the other.
3. Bioelectric potential refers to the difference of electric potential between the inside and the outside of a cell.
4. The ratio of the zetacrit to the hematocrit, used as an indicator of the red blood cell sedimentation rate.
5. The potential developed across any interface separating two phases as a result of the accumulation of electrons in one phase and the loss of electrons in the other direction.

The ratio of the zetacrit to the hematocrit, normally 0.41 to 0.54 (41 to 54%); used as an indicator of the red blood cell sedimentation rate.

It is a sensitive indicator of the erythrocyte sedimentation rate (ESR) and is unaffected by anemia, which tends to elevate the ESR.