stands for long polyp stony coral, SPS
is for short polyp stony coral. Both of these types of coral have a hard skeleton, which the individual polyps protrude from. The difference between the two is basically just the length of the polyp. SPS
polyps are very small, whereas LPS
polyps can stretch to 6 or 7", depending on the type of coral.
Any soft coral, is one that lacks any type of calcareous skeleton, like Leathers, Zoanthids, Mushrooms, Xenia, Palythoas, Colony polyps, etc.