enque/top_list_length is a SAP Parameter attribute which is used to control Length of the top lists in case of table overflows 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 .
If there is an overflow of the lock table, statistical information about
the owners of the locks is written to a file as a list. This file can be
used to identify the application that caused the overflow. This
parameter controls the length of this list.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.