Spinnbarkeit is a medical term and refers to the stringy and/or stretchy quality found to varying degrees in mucus, saliva, and similar fluids. The term is used especially with reference to cervical mucus at the time just prior to or during ovulation.
Under the influence of estrogens this mucus becomes abundant, clear, and stretchable, somewhat like egg white. The stretchability of the mucus is termed spinnbarkeit, meaning in German that it has the ability to be spun. Only such mucus appears to be able to be penetrated by sperm. After ovulation, the character of cervical mucus changes, and under the influence of progesterone it becomes thick, scant, and tacky. Sperm typically cannot penetrate it.
Saliva does not always exhibit spinnbarkeit, but it can under certain circumstances. The thickness and spinnbarkeit of nasal mucus are factors in whether or not the nose seems to be blocked.