The term hermetically sealed is used to describe something that has an airtight seal. The term is often used to describe electronic parts that are designed and intended to be secure against the entry of microorganisms and to maintain the safety and quality of their contents. Applications include thermostats, optical devices, switches, and other devices. The food, chemical, and medical industries all have applications for the use of such "airtight" packaging, as well. High-end coffins, too, are often made to be "hermetically sealed," and must be of metal, or of other material with metal lining, and constructed so that when closed and fastened the coffin is completely airtight. A microorganism or microbe is an organism that is so small that it is microscopic (invisible to the naked eye). ... A thermostat is a device for maintaining the temperature of a system within a range by controlling the flow of heat energy into or out of the system. ... This article is about electrical switches. ...

The expression "hermetically sealed" finds its roots from Hermes Trismegistus, who was said to have been the Egyptian god of wisdom, Thoth. Its origin can be traced back to about 300 AD. Hermes purportedly authored several books containing secrets of alchemy and mystic philosophy. One such secret contained in his works was how to create an airtight vessel. His "hermetically sealed" container employed the use of a vacuum pump. This article needs cleanup. ... Thoth, pronounced tot, is the Greek name given to Djehuty, the Egyptian god of the Moon (lunar deity), wisdom, writing, magic, and measurement of time, among other things. ... For other uses, see number 300. ... A vacuum pump is a pump that removes gas to leave behind a partial vacuum (of varying quality, depending on the pump). ...