Definition - What does Fine Lees mean?
After fermentation is complete and a wine has been racked a couple of times, there are still some solids which remain behind. These solids are fine lees. When wine is aged, the lees, which settle at the bottom of their aging vessel, can add character and depth to wines.
WineFrog explains Fine Lees
Fine lees are a natural occurrence in wine and are the left-over particulates which are suspended in wine from grape skins and yeast cells.
Larger lees' particulates are racked off a couple of times following fermentation, but the leftover lees are finer and can be beneficial to the wine.
In the case of reds, aging wine on lees is not a common practice. For red styles, even fine lees can make a wine bitter and astringent. However, for white wines, aging on fine lees add aromatics and texture to the wine. They make a wine softer and with a fuller mouthfeel. They also add certain aromatics like stone fruit, cream and a touch of yeasty characters like bread dough or fresh-baked bread.