This is one I often get caught out with. I did a science degree and often find that stuff I say is misinterpreted by non-sciency people.
A paper published by Physics Today (there's a summary chart at BoingBoing) says that scientists need to be more considerate of the words they use and take into account colloquial meanings. I'd say that many Lifehacker readers would have studied or worked in technical disciplines where words carry a different meaning.
What's something that's in common parlance in your profession that has a different meaning to lay-people?