Leadはまさに先行するもの、という意味だと思います。すなわちいずれ買ってくれるであろう者。
on-line辞書には以下のように載ってます。
A sales lead is the identity of a person or entity potentially interested in purchasing a product of service, and represents the first stage of a sales process.
Sales leads come from either marketing lead generation processes such as trade shows, direct marketing, advertising, Internet marketing or from sales person prospecting activities such as cold calling. For a sales lead to qualify as a sales prospect.
お礼
非常に良く理解できました。ありがとうございました!