What is in-situ concrete?

In-situ concrete is concrete which is used and processed directly on the construction site, i.e. in-situ, as fresh concrete. It is mainly used if very large parts or areas have to be made from concrete. In such cases, the transport of prefabricated parts would be much more complex than the use of fresh concrete. In-situ concrete is used in plastic form and then has to harden on the construction site before it is possible to continue building and working with the parts or areas thus produced. In-situ concrete is used for the construction of house foundations and machine beds.

More about this on https://www.dornbach.com/de/baulexikon/ortbeton.html