transport/during_upgrade is a SAP Parameter attribute which is used to control Flag for Transportsystem to work upgrade-specific information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
Switches the work directory of the log writer from DIR_TRANS to DIR_PUT.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.