Good news for audiophiles! We've started to introduce audiophile FLAC availability on select titles. FLAC is is becoming the industry standard for audiophile quality digital music. These are BIG files that offer sound equal to, or, in some cases, even better than cds.
FLAC (Free Lossless Audio Codec) is a codec (compressor-decompressor or coder-decoder) which allows digital audio to be losslessly compressed such that file size is reduced without any information being lost. Read more at Wikipedia.
There are a growing number of audio devices that allow direct playpack of FLAC files. Currently, FLAC files do not open natively in iTunes, but there are many methods to convert your files to allow playback in your iTunes library for both Mac and PC users. Some are in the form of a simple pluggin which handle the conversion automatically within iTunes. There are tons of great articles on the web on this topic. Here's one from the popular site Gizmodo.