As one who makes his living in sales, I would disagree with the idea that "lead" and "prospect" are the same.
Granted, a "lead" and a "prospect" are both persons from whom you hope to close a sale. However, (and this is a very important distinction), a "prospect" has given you some form of commitment in terms of time, energy, activity, or money. A "lead" is, as of yet, without a commitment.
So, one could think like this:
A "lead" is someone from whom you hope to close a sale.
A "prospect" is a lead who has demonstrated, through action, a commitment of time, energy, activity, or money, but has not yet closed the sale.
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It may seem for some that making this distinction is splitting hairs, but "being successful in sales" is predetermined by this keen ability. The salespeople who know "who's playing ball with them" are the ones who make six figures or more.
(And for anyone who cares, Stephen Schiffman is a terrific mentor in helping you determine who your real "prospects" are. See any of his books at Amazon.com, e.g., "Getting to Closed".)
Warmest of regards