Definition - What does Heavy mean?
Heavy is a wine descriptor used to note many different things, but it is most often used to in relation to the wine’s feel in the taster’s mouth, also called "mouthfeel". When used to describe wines, the term heavy typically means that the wine feels viscous and full, which is caused by a higher alcohol content. A heavy wine will usually have an alcohol content that is above 12.5% and have a more concentrated structure of flavors.
WineFrog explains Heavy
A heavy wine can also mean that it is a wine with a full body and a higher alcohol content. These wines are substantial in their tannins, flavors and pigments. In general, heavy wines are full-bodied red wines like Cabernet Sauvignon, Syrah, Tempranillo and Malbec. They achieve their heaviness and higher alcohol content when the winemaker adds more sugar during the fermentation process. The wines won’t be sweet; they'll have dry, earthy, bitter and fragrant flavors and textures that pair well with bold flavorful meals.