A mold (US) or mould (UK / NZ / AU / ZA / IN / CA / IE), also referred to as mildew, is a fungus that grows in the form of multi-cellular filaments called hyphae (long, branching filamentous structures). In contrast, fungi that adopt a single-celled growth habit are called yeast. Mold is present almost everywhere, including the air. The term mold is often used in non-scientific context to describe many types of unwanted fungi. For the most part mold, like most fungi, break down plant and animal matter in the environment. To reproduce, molds release spores that can spread through air, water or on animals. Some mold produce mycotoxins, chemical components of their cells walls, that can pose serious health risks to huumans and animals. (see: Wikipedia).