HDCD is a propietary system for recording more than 16/44 onto a regular CD. HDCD discs can be played back on an ordinary player and the effect is a bit like analog compression. Played back on an HDCD compatible player, the effect on well produced CDs (like Ref classicals) is startling. However, many HDCD encoded discs (like lots of the Rock stuff, e.g. Mirror Ball?) sound so processed anyway that the HDCD process almost seems irrelevant.
