J.R. S. answered 04/15/21
Ph.D. in Biochemistry with an emphasis in Neurochemistry/Neuropharm
These terms (along with others describing solubility) are rather arbitrary, but here is a general (and I mean general) rule of thumb.
Soluble: 1 g dissolves in less than 30 mls of solvent
Sparingly soluble: 1 g dissolves in 30 - 100 mls of solvent
Slightly soluble: 1 g dissolves in 100 - 1000 mls
Insoluble: 1 g dissolves in >1000 mls (Some would say >10,000 mls and anything from 1000 mls to 10,000 mls would be very slightly soluble. Really!!!)