What does 'Spin-up', 'Ramp-up' and 'Pre-run' mean?

Hi,
I’m beginner of wrf-smoke-cmaq model.
I wonder what the difference is because the concepts of ‘Spin-up’, ‘Ramp-up’ and ‘Pre-run’ look similar, but they will be marked differently.

Spin-up refers to how CMAQ starts with a “clean” initial conditions concentration and runs for approximately 2 weeks, after that point, the effect of the “clean” initial conditions is reduced. The Start Date of the modeling can proceed using well-mixed atmospheric conditions that take into consideration meteorology, chemical reactions, and emissions.

I am not familiar with the terms “ramp-up” or “pre-run”.

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