Yeah its probably one of those concepts that is best explained by explaining what it is not .
Work trains , deadheads, driver training etc are not revenue service trains .
"General Discussion: About RAILROAD.NET" is for questions about this web site. I moved your post to "General Discussion: Railroad Operations and Facilities."
"Revenue Service" is any train that makes money for the railroad. This includes hauling passengers or freight- services they can collect money for.
Non-revenue service includes work trains, deadhead movements, and other trains for which they cannot charge money to offset the costs of operation.