Correct me if I am wrong, but I think that compressibility, generally tells how difficult it is to compress an object. Meaning, the higher the compressibility, the easier it will be to compress an object with a given pressure. I was asked in my University to describe an system of infinite compressibility. I think that would mean that the volume changes would be infinite with the exercise of least pressure. Does a system like that exists? I couldn't think of anything.