Balsamic vinegar is a specialty vinegar from Modena, Italy made from Trebbiano and Lambusco grapes. There are strict guidelines for production of this vinegar but due to the immense popularity you may find low-cost, low-quality products on the market. The longer the vinegar is aged, the more expensive it will be. Vinegars aged 25 years to 100 years vary in price from from over $100 to over $200.00 for a 3-4 ounce bottle.
The vinegar is thicker than other vinegars, dark, almost black in color and it has a sweet, full-bodied flavor. In its finest aged form it can be consumed like an aperitif but it is most commonly used as a base for salad dressings and sauces, and reductions. You the read more about the production and aging of Balsamic vinegar.
There is also a white balsamic vinegar which works well for dressings you don't want colored by the dark balsamic. It does lack the depth and flavor of aged balsamic.