The precise definition of a 'lead' tends to vary somewhat. In fact, one of the biggest stumbling blocks between sales and marketing can be the definition of what counts as a lead and what doesn't. It's important to make sure that everyone involved in lead generation is in agreement with the people responsible for following up on those leads.
Most salespeople define a lead as someone who matches the criterion the salesperson has established and who has the need, reason and/or interest in pursuing the product.