You remember this phone service: the speaking clock? In case you're too young to know such a thing exists, it's a robot that gives you the exact time when you call it.
Now imagine we want to make this service unusable for people (denying it). We'll ddos the robot by dialing its number all day long. If there are enough kids doing it at the same time, the speaking clock will be unable to receive new calls, being effectively ddosed.
Then, loic is just an automatic dialer.