Plumbing water line and drain schedule
Pipe schedule is a standard way of specify the thickness of the wall of the pipes.  There is code that requires minimum schedule pipe and approved materials for drains and pipes.  Code varies by location.  They probably want you to specify something like

MIN. SCH 40 ABS 3" DRAIN PIPE


On your plans.  You could also ask the city to show you some example plans.  Or even go in to the office in person and ask about meeting with your plans reviewer, if nothing else.  In my city they encourage you to do this before submitting them.