In situ (/ɪn ˈsɪtjuː/ or /ɪn ˈsaɪtʃuː/; often not italicized in English) is a Latin phrase that translates literally to "on site" or "in position". It means "locally", "on site", "on the premises" or "in place" to describe an event where it takes place, and is used in many different contexts. For example, in fields such as physics, chemistry, or biology, in situ may describe the way a measurement is taken, that is, in the same place the phenomenon is occurring without isolating it from other systems or altering the original conditions of the test.

Aerospace

In the aerospace industry, equipment on-board aircraft must be tested in situ, or in place, to confirm everything functions properly as a system. Individually, each piece may work but interference from nearby equipment may create unanticipated problems. Special test equipment is available for this in situ testing.

Archaeology

In archaeology, in situ refers to an artifact that has not been moved from its original place of deposition. In other words, it is stationary, meaning "still." An artifact being in situ is critical to the interpretation of that artifact and, consequently, of the culture which formed it. Once an artifact's 'find-site' has been recorded, the artifact can then be moved for conservation, further interpretation and display. An artifact that is not discovered in situ is considered out of context and as not providing an accurate picture of the associated culture. However, the out of context artifact can provide scientists with an example of types and locations of in situ artifacts yet to be discovered. When excavating a burial site or surface deposit "in situ" refers to cataloging, recording, mapping, photographing human remains in the position they are discovered.