Journal created by MSC Patran, a pre and post-processing program for Finite Element Analysis (FEA); contains any commands related to the database that have been executed while creating a specific model; it's similar to the .SES file but includes every command for all the sessions of the model and the specific database.

Do not delete the DB.JOU file because it makes it possible to recreate an entire .DB from nothing. If you lose your database, you can recreate it by selecting File → Utilities / Rebuild..., navigate to the appropriate DB.JOU file, and click OK.