SC4 "stereo" stereo meaning..?

what does stereo mean in reference to the sc4 compressor? (it states it’s a stereo compressor) does the track need to be stereo for the compressor to work right/or does it just mean it can compress stereo tracks/independently and such (as well as mono)?

It means that gain reduction due to a peak in one channel of a stereo track will be applied to both channels. Doing so maintains the original stereo image, whereas processing the channels independently can cause the stereo to swing from side to side.

The effect may be used on mono or stereo tracks.

Thanks Steve--------so is the other default Audacity Compressor the same–per it being applicable for stereo or mono and when stereo–designed to maintain original stereo image…(etc.)?

Unfortunately no. The built-in Audacity compressor processes each channel separately. In most cases this will not matter because usually the left and right channels of a stereo track are quite similar, but in cases where the left and right channels are very different the stereo image may not be completely stable. Even with this limitation, unless very strong settings are used, this downside will probably not be noticeable.