Tau proteins (or t proteins, after the Greek letter by that name) are proteins that stabilize microtubules. They are abundant in neurons of the central nervous system and are less common elsewhere, but are also expressed at very low levels in CNS astrocytes and oligodendrocytes. Pathologies and dementias of the nervous system such as Alzheimer's disease and Parkinson's disease  are associated with tau proteins that have become defective and no longer stabilize microtubules properly.