In situ is a Latin phrase meaning 'in the place' or 'on site', derived from in ('in') and situ. The term refers to studying or working with something in its natural or original location rather than moving it elsewhere. This approach preserves environmental factors and relationships that might be lost when materials or specimens are relocated to controlled settings. In comparison, ex situ methods involve removing materials or specimens for study, preservation, or modification under controlled conditions, often at the expense of their original context. The earliest recorded use of in situ in English dates back to the mid-17th century. Its use in scientific literature expanded from the late 19th century onward, beginning in medicine and engineering, and later spreading to a wide range of disciplines.