All fungi, which show also a series of ecological mutualities mainly morphologic, however, are called molds.
They distinguish yourself in that they have a cotton wool-shaped one, fädrigen or powdery look (moldy) on the surface. This is caused since the growth takes place not only in the material-inside but at the surface. However, there are also bacterias, who show a fungous look with the growth. To this, the so-called radiation-fungi or Actinomyceten belong.
One can accentuate to the characterization of the molds:
Aspergillus and Penicillium (picture 2.1.1.) they are at the farthest spread molds. They belong family Eurotiaceae Euascomycetidae, order Eurotiales, to the department Eumycota (real fungi), class Ascomycetes (hose-fungus), lower class. All is milk unda Saprotrophe, therefore fungi, which lives from dead, perished or artificially synthesized organic substrates, for example on food, like bread, fruits, itself. The fungi develop a quite typical real Myzel which richly is branched and stretches in the substrate or on its surface.
Form 2.1.1.: Penicillium (brush-mold) 
Its augmentation takes place almost exclusively through asexual Mitosporen (anamorphe Fruktifikation), through formation of endospores (Sporangiosporen) or exospores (conidiums), occasionally Chlamydosporen. The conidium-bearers are quite typically shaped in each case and offer the most important differences. So, the conidium-forming hyphas finish in a blister, that is intensively covered with small rod-shaped unicellular organs and Sterigmen is called, with Aspergillus. The conidium-bearers of Penicillium branch at the apex in thin little branch. Everyone this little branch carries a Sterigma, that becomes bekrönt from a conidium-chain. The Myzel is more or less colourless. The conidiums carry dyes, that its specific coloring the fungus-colony, black, brown, green, yellow or white with Aspergillus and primarily blue-green with Penicillium (also green-mold), lends. With Aspergillus, the tone of trace elements is dependent in the found substrate. for example Aspergillus nieger colors intensively black (also black-mold), if copper is present, otherwise it assumes a light yellow coloring.  Since the reproduction takes place almost exclusively through the above named conidiums, no showy fruit-bodies are produced. If at all sexual reproductive organs are formed, then only minutely small.
Gets Zellsprossung and formation of sprout-cells, as they characterize yeasts or yeast-similar fungi, only in quite rare cases under certain conditions.
Its habitat is the ground preferentially, also other habitats are able to conquer, like moist spaces or climate-zones.  includes links with boiling points of 0 - 250 ºC the characteristically transient metabolites of mold MVOC (Microbial Volatile Organic Compounds) and can be assigned a wide spectrum of different chemical material-classes, like for example the alkanols, Alkenolen, ketones, Terpenes, Aldehydes, alkanes, sulfurous links, Ethenen, ester, Karbonsäuren unda. It became about until 2001. 30 such links in interiors and in the outside-air proved, that can be formed by molds. 
The musty smell is to frequently be led back on the formation of MVOC through molds or bacterias. Following spectrum of links is characteristics:
3-methyl-furan, Geosmin, 1-Octen-3-ol, 3-methyl-1-butanol, 2-Pentanol, 2-Hexanon, 2-Heptanon, 3-Octanon and dimethyl-disulfide.  in higher concentrations shows a toxic effect some MVOC. In the interiors, low values, that don't contribute to any health encroachment, usually are available. The meaning of the MVOC is not yet sufficiently explored.  It, to also heed, is, that all transient metabolites, that are produced by microorganisms, don't come only from microbial origin. You/they are produced also by plants, is element of aroma-materials and technical solvents.