Leading and Lagging Indicators for Cogeneration Power plant

Dear sirs/Madam,,

I am currently developing the Leading and Lagging Performance Indicators for a Cogeneration-Combined Cycle Power plants with 8xGTGS, 8X110TPH HRSGS (VHP Steam),4x400TPH UB (VHP Steam) and 4XSTGS with HP and MP steam Extraction cum Condensing steam turbine. There are also VH-HP PRDS, VHP-MP PRDS and MP-LP PRDS (Pressure Reducing Desuperheater).

Now my questions are:

1. I need broad explanation on what Leading and Lagging Performance Indicators are.

2. I will appreciate if anyone can list out possible leading and lagging performance indicators for such a plant as my own above.

Thank you