Definitions

Name	Cause	Physical Process	Spectroscopic Signature
Core dimming	Mass loss	Ejection of emitting plasma from corona	Simultaneous drop of multiple emission lines, with roughly the same percentage decrease
Thermal dimming	Temperature evolution	Heating raises lower ionization states (e.g. a fraction of Fe IX becomes Fe X), cooling does the opposite	Heating: Emission loss in lines with lower formation temperatures with roughly simultaneous emission gain in lines with higher formation temperatures. Cooling: reverse of above
Obscuration dimming	Obscuration	Dim feature (e.g. filament) moves between observing location and bright feature (e.g. flare arcade)	Drop of emission lines proportional to their absorption cross section in the obscuring material. Also apparent in EUV images
Global dimming?	Waves	Shocks propagate globally, causing compression/rarefaction of plasma	Apparent in EUV images, especially using difference movies
Doppler shift dimming	Doppler shift	Fast moving plasma causes Doppler shift of emissions, which could start to shift outside instrument bandpass	Doppler shift is seen in spectral measurements (e.g. EVE)

This is a good place to have the debate about names and the expected spectroscopic signatures. It'd be best to use the comment section below until we reach a consensus, and then we can update the table.