A marketer develops campaigns designed to reach out to those potential buyers; most typically with a call to action. If a potential buyer (prospect) responds to that call to action, marketing calls this a "lead" and counts this as a feather in their cap. After all, marketers take a holistic approach to their craft. They are chartered with "making the phone ring" and use different mechanisms such as direct mail, email campaigns, trade shows, seminars, etc. to do so. Marketers measure success by "hits," attendees, inquiries, etc., then try to equate a Return on Investment (ROI) to such metrics. Typically, this ROI is based on sales pipeline or projected sales which may take months or even years to materialize. While there is value in these marketing initiatives, quantification of value is in the eyes of the beholder.
Sales people are much more tactical and only focused on the numbers that really count—compensation for their efforts. In most organizations, sales people view leads much differently than marketing. They view them as opportunities to close business in a defined (the shorter the better) time period. A lead needs to be qualified.
The problem is in the definition of a "lead" and the definition of "qualified."
You have two groups of people with different backgrounds, different objectives, and different definitions. In order to function properly, these two groups need to communicate more effectively. They need to share a common lexicon, a common dictionary, and a co-dependent level of accountability.
Of the two groups, marketing is more likely to have the advanced educational degree, work in the corporate office and be focused on metrics one or two steps removed from the heart of the sales cycle. They view leads as opportunities and the more the better.
Sales is much more primal. They think: "Is someone ready, willing and able to buy my product now?" These are relationship people and risk takers who are more likely to have been the quarterback on the football team or the captain of the baseball team. They are in the field and work directly with the customer.
Because of where they come from and how they are measured, a rift is inevitable. Marketing creates all this great activity and thinks "these dumb jocks can't sell their way out of a paper bag." Sales looks at marketing and says "these poindexters wouldn't know a good lead if their life depended up it."
However, the common ground is that both sales and marketing need results to survive and prosper. They each need to contribute to corporate objectives, but take very different paths to get there, with many collisions along the way.