"Invalid click activity consists of any clicks or impressions that may artificially inflate an advertiser's costs or a publisher's earnings, and for which we decide not to charge the advertiser. This includes, but is not limited to, clicks or impressions generated by a publisher clicking on his own ads, a publisher encouraging clicks on his ads, automated clicking tools or traffic sources, robots, or other deceptive software.

Please note that clicks on Google ads must result from genuine user interest, and any method that artificially generates clicks or impressions is strictly prohibited by our program policies."

That's directly from their AdSense help.

As for not being able to apply again that's not true. If you are banned then yes you can't reapply (with the same name at least), but I have had my other blog turned down 5+ times and I was able to reapply every time. My reason was I didn't meet their program policies although they never explained what exactly I wasn't meeting.