You better ask the original devloper/contractor/architect or vendor of this database.
Temp data typically is in the temp database, not in a database owner schema of a database with prefix tmp. This is not a SQL Server system table either. So it's mainly a question about the definition or meaning of this prefix in the database of your specific application, not a question SQL Server administrators or developers could answer you. One thing is right, tmp typically indicates temporary data. But as said the place for temp data rather is the temp database and so the meaning may not be very literal. I inherited some apps using "temp" Tables to store configuration/last choices, current project etc. between application sessions.
Now you need to get sure about whether you want to truncate the table or not. Depending on the recovery model of the database each operation is logged or not. You may remove all data, you may (kind of) only move it from mdf to ldf file, from core database file to transaction log. So if this is about freeing some hdd space, you better learn about the transaction log first. Until then I'd not truncate the table, having no concrete knowledge about what the app does with it and whether you really get back space or not. Even shrinking the database afterwards is not necessarily shrinking the log file.
Bye, Olaf.