People who cannot be bothered to cover the simplest basics of a topic on their own. It's usually hard to explain anything to them because anywhere you try to start from they will need you to explain that topic first, and on, and on. If you ask them "what do you understand" in an attempt to join them in some common frame of comprehension, they look at you with a blank stare and reply "what do you mean". That's how they drain you of your life energy. Help vampires.

Essentially, someone who asks continual questions and who seems unwilling to do any work, research, or to put any effort into learning on their own. Overview is here:

http://meta.stackexchange.com/questions/19665/the-help-vampi...

A common variation is someone who asks a reasonable question, gets an answer, then repeatedly modifies/extends the original question, or who asks a long series of follow up questions n comments. This variation is described here:

http://meta.stackoverflow.com/a/258279/1441122

Help vampires are people who suck the life out of those who answer questions. They ask questions without bothering to think about it themselves, often without enough information to actually answer the question well. These types of questions are frustrating to answer, and lead to people assuming the worst of new users who ask bad questions unintentionally.

It's a sliding scale. Most people just don't know how to ask a good question initially, but some just don't care. In general, I'd say the 'help vampire' problem is where the asker is looking for the answerer's time, not their help. They want someone to do free work for them, without putting in effort themselves.

I believe this is the origin: http://slash7.com/2006/12/22/vampires/