What exactly does Moe mean?

I believe it means cute

It's actually really hard to explain
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It's similar to saying cute, или at least cute is the closest word in English. It's usually referring to one specific trait ex. glasses.

If someone says someone in general is moe they usually mean that they're lovable, make Ты feel like taking care of them, not totally independent etc.

I'm not 100% sure (try asking someone who does think of this) but people might think Kanade is moe because by the end of the series Ты do want to take her in an hug etc. she's just one of those characters.