sec/libsapsecu is a SAP Parameter attribute which is used to control complete path and filename for SAPSECULIB 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 .
This parameter configures the path of SAPSECULIB that is delivered by
SAP.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.