J2ME is all of mobile
Java, as opposed to J2SE or
J2EE. However, because all mobile devices are different (phones, PDAs, toasters, TVs), as opposed to desktops or servers, one size does not fit all. Instead J2ME is broken into "lego-like" pieces.
As the base level are two configurations, CDC and CLDC. The former is for "always connected" devices, like TVs, washing machines, and automobiles (stable radio connection). CLDC is for phones, pagers, PDAs, etc.
On tope of that are profiles. A PDA is very different then a pager. Even an iPaq is different from a palm in terms of abilitiy. Different profiles allow you to get the most of the device.
See Sun's J2ME pages for more info.
--Mark