Well there is actually a billion of moe definitions... one of the most easiest is "its something that makes otaku heart make doki-doki" mostly is meant in non perverted way but its not a rule at all.
Moe anime have characters with even bigger eyes than usually and with a lot of of poses that are usually referred to as kawaii but the poses are usually extreme and animators like to exaggerate while using them (otherwise is not moe at all). one of those first but really cute moe anime is AIR TV ... i believe lots of you know this one. Lots of girls is a must (personally i like to call moe and extension of harem anime), guys are rarely called moe. Well most of them in Clannad are moe (especially the blond guy - but he's annoying <.< so he's not a perfect moe XD).
But overall there is no THE definitions - there are some common points but the rest is mostly up to a person itself to explain what moe exactly is - or at least that is a far i managed to understand what moe is -.-;;
Chibi