"Business Development" seems to mean totally different things at different companies. I recently found this old Seth Godin post on the topic. His explanation is instructive and clarifying - here's a short excerpt:
"Good business development allows businesses to profit by doing something that is tangential to their core mission. Sometimes the profit is so good, it becomes part of their core mission, other times it supports the brand and sometimes it just makes money. And often it's a little guy who can be flexible enough to make things happen."