 <p>1) Assuming you want your key to be unique, have you considered how you will handle this using a standard field? There is no out-of-the-box way to enforce uniqueness with a standard field. There is an <a href="http://success.salesforce.com/ideaView?id=08730000000Bqct" rel="nofollow">Idea Exchange request</a> for such a feature.</p> <p>That said, you can create a custom field that accepts the value from a standard field (via a workflow or trigger), and force the custom field to be unique.</p> <p>You can also just use a custom field and not use the equivelant standard field: per your example. you could easily create a custom field with the label "Email" and simply hide the standard Email field from the page layouts and/or profiles.</p> <p>2) Standard fields definitely have <a href="http://www.salesforce.com/us/developer/docs/api/Content/sforce_api_objects_contact.htm#topic-title" rel="nofollow">API names</a>.</p> <p>3) Are you asking for the definition of a <a href="http://en.wikipedia.org/wiki/Key_field" rel="nofollow">key field</a>?</p>