A zone of apposition between the membranes of an organelle with another membrane, either that of another organelle or the plasma membrane, structured by bridging complexes. Membrane contact sites (MCSs) are specialized for communication, including the efficient traffic of small molecules such as Ca2+ ions and lipids, as well as enzyme-substrate interactions. [ http://www.ncbi.nlm.nih.gov/pubmed/16806880 ]