Like the tale of the blind men and the elephant, the business development role can be quite difficult to define. Depending on the industry, the company, and even the wishes of the CEO, "biz dev" people can fill many functions: sales or corporate partnerships or mergers and acquisitions.

“Senior sales people are often called business development,” says Joseph Lassiter, professor of management practice at Harvard Business School. “They’re the Navy SEALs of sales; the special-forces team.”

That said, business development personnel also fall into a few categories, says Lassiter:

• They're fundamentally smart sales people that understand and cover a wide range of industries.

• They sell custom stuff to custom people.

• They can get you into a lot more trouble than a conventional sales people.

Why? Whereas the normal sales executive worries about making his or her numbers on a quarterly basis, the biz dev exec has a lot more to win (or lose) when trying to close a strategic partnership or outright acquisition. (Says one investment banker-turned-biz-dev guy: “The dirty little secret of M&A is less than 50 percent of the deals actually create shareholder value.”)

But the best biz dev players do more than just make deals, Lassiter says. They keep the relationships running smoothly:

“Imagine, if you can, a company as a cube with three faces and each face is two-sided—customers, old and new; partners, old and new; products, old and new. Business development people tend to work on the partner side of the cube, and anytime you need new partners or if there is a complicated relationship with old partners, business development people manage those partnerships,” says Lassiter.

Also, a great business development executive doesn’t blow his own horn, he says. The good ones don’t want to alert the competition or upset the rank and file of a company they are looking to work with or acquire.

“I know a company where the lead BD guy has as his title 'regional sales engineer' because he doesn’t want to attract attention,” says Lassiter. “The title has enough weight to get him through the door, but it's not big enough to set off any alarms; he attracts no attention.”

“The good ones,” says Lassiter, “are a joy to watch.”