A Capillary Break in construction is the use of a hydrophobic material (non-porous material) that acts as a barrier between two layers of material that is able to stop capillary action.
Capillary Breaks are used to prevent water from entering a building, damaging materials, and causing structural issues. Capillary breaks are incredibly important and are the first line of moisture defense in buildings. While the capillary breaks are generally referred to in the context of concrete foundations it is important to note that capillary breaks are also present in windows, doors, EIFS systems, curtain walls, and more. If a component is on the exterior of a building and is subject to the elements that it will most likely have some form of capillary break, or there will be a reason a capillary break isn't necessary.
Layer of gravel preventing moisture from rising into concrete.