Mouthfeel refers to how the wine feels in your mouth. The sugars, acids, alcohol, tannins, and various other components in the wine will affect the way it coats and interacts with your mouth.
Sweeter wines, such as dessert wines, will have a softer, syrupy mouth feel more than a dry wine. A full-bodied red wine, higher in tannins and alcohol, with have more of an edge – almost a bite – as it hits your taste buds, and moves around on your tongue.
Generally speaking, wines with a softer or smoother mouthfeel tend to have a longer, lingering finish, and the wine will evenly coat your tongue, just as it will your throat when you swallow it.