Zalgo is a fictitious entity created for an edited comic strip.
Zalgo is represented as a malign chaotic entity who manifests as apparently corrupted text on web pages, and as a black tentacled mass within cartoons and other images.
The apparent corruption of text is accomplished by using accent marks and other meta characters. If the viewers browser is using the correct character encoding, the text is readable, other wise the marks are displayed in a manner that makes the page unreadable (often with a vertical stacking of the marks running down the page.
When people attempt to find out what Zalgo is, members of the internet community often reply with this phrase (or sections there of):
"Zalgo is To invoke the hive-mind representing chaos.
Invoking the feeling of chaos. With out order.
The Nezperdian hive-mind of chaos. Zalgo.
He Waits Behind The Wall..."
This explanation is offered up to further confuse the asker instead of help them. This childish behaviour is widespread and serves to alienate those who don't realise that there is little more to the meme than the use of a simple idea to confuse people.
"What is Zalgo?"
Usual Answer: "To invoke the hive-mind representing chaos. Invoking the feeling of chaos..."
Useful Answer: "An internet meme that goes unexplained all too often as the internet is full of teenage virgins who like to feel superior by pretending to know something"