A zone of apposition between the membranes of an organelle with another membrane, either another membrane of the same organelle, a membrane of another organelle, or the plasma membrane. Membrane contact sites (MCSs) are structured by bridging complexes. They 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 GOC:jl ]