Moe is a slang word. There is a literal definition. It means
budding, and refers to plants.
In anime it can have many meanings but with a common factor.
People feel protective of moe characters.
Moe characters are always lovely, whether they be maids, cat
girls, girls in glasses or whatever. Often they combine innocence
and childlike characteristics with bodies that can easily be
sexualized.
The true moe fan wants to preserve their innocence. This is not
lolicon. Most moe fans agree that blushing is cuter than a panty
shot. Some will even find the panty shot vulgar and still like moe
characters.