These extracts are made by passing carbon dioxide through aromatic plant material. The CO2 is in a “supercritical” state, meaning it has the properties of both a liquid and a gas. This is because of the specific pressures and temperatures used. In this state, it acts as a solvent and extracts aromatic molecules, which are then separated from the gas. You can see the whole process illustrated here: https://youtu.be/oJa8dzE0LqE
The composition of a CO2 extract is generally different from the equivalent essential oil. Because of these differences, CO2 extracts can have distinct therapeutic properties. For example Ginger CO2 contains gingerols, constituents that give ginger its pungent taste. Gingerols are especially effective in treating nausea (yet caution is needed when using Ginger CO2, as gingerols also tend to be skin irritants).
There two principal types of CO2 extract – select and complete. Select extracts are generally more similar to essential oils, and total extracts contain more heavier molecules and could be compared to absolutes.