Astringency

A dry, rough, tactile sensation perceived in the mouth, not only on the tongue but also on the palate and gums.

This sensation arises when the lubricating qualities of our saliva diminish in the presence of polyphenols, tannic substances found in wood.
Polyphenols tend to bind to mucin, a protein found in saliva, causing it to drop.
It is a term commonly used in the context of wine, and described as the tactile sensation of dryness and dehydration of the palate, characteristic of tannin-heavy wines.

In the case of coffee, it may result from mistakes made during harvesting (beans harvested from unripe fruit), underdeveloped roasting profiles (too light a roast) or over-extraction (over-exposure of the ground roasted coffee or part of it to water during the extraction process).