They are the cannabis plant’s trichomes – the tiny, crystalline hairs that grow on its flowers and leaves – that have been extracted using one of several methods. The goal of every concentrate is to remove all impurities and leave behind a pure product that contains nothing but the cannabinoids and terpenes (the molecules responsible for flavour and aroma) that you want.
There are several methods of extraction, but they all have the same goal: to isolate the trichomes from the plant matter and create a highly potent product. The most common methods of extraction include solvents (such as butane or CO₂), water, and ice water. Cannabis concentrates are much more potent than regular weed, usually it goes around 50-95% THC depending on the type.