Blackberry concentrate is a thick liquid made from pressed, condensed blackberries. The main draw is a high concentration of anthocyanins, the same pigments that give the berries their dark purple color. Processing strips out the fiber found in whole fruit, so that benefit is lost.
Most people stir a measured amount into water, smoothies, or yogurt once or twice a day. The liquid form makes it easy to blend into drinks with no grainy texture.
Watch the sugar content. Sweetened concentrates pack a lot of sugar. Stick to unsweetened versions if you are managing your blood sugar. Potency and quality jump around a lot from one brand to the next, so read the label closely.