A visitor lands on your website through a Google search or social link. He or she is now a prospect. The visitor might check out a few of your blog posts or browse your product listings. At some point, you offer him or her a chance to sign up for your email list.
If the visitor fills out your form, he or she becomes a lead. You can now market to the customer outside of your website, such as via email, phone, or text — or all three.