dbs/db2/use_define_no is a SAP Parameter attribute which is used to control DB2: switch for usage of DEFINE NO 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 set to 1 all tablespaces and indexes are created with storage
attribute DEFINE NO.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.