So I see language like this in discussions about headphones. What are the numbers? At what ohms would a headphone considered low, and what would be considered high? Or what ranges?

On the MMCX end of the IEM cable, is the center pin typically the positive terminal, with the outer portion the negative? I can use a multi-meter to figure out which is which when I cut off the fixed single ended plug, but I then need to know the polarity to re-terminate properly. BTW folks...

Actually I think I mean 2.5mm, not 3.5 mm. Does anyone know what these are commonly referred to as, if I wanted to search for them to make an adaptor? The plug I am referring to is the one that looks essentially like a normal IEM male plug but has 4 connection points instead of the standard 3...