Leads
Leads are prospects that are not yet real deals. They live in their own inbox so that unqualified interest does not clutter the pipeline.
/leads is the list; /leads/[leadId] is one lead.

Opening a lead from the list shows it in a slide-over panel over the list rather than navigating away.
What a lead holds
A lead has a title, an optional value, a source, and links to a person and an organization. Labels and owners work as they do on deals.
Linking to contacts
A lead links to a person and an organization. On import, those links are resolved find-or-create, so a lead for an existing company attaches to that company rather than creating a duplicate.
Converting
Converting a lead creates a deal from it, carrying across its value, contacts, and labels, and takes the lead out of the active list.
Conversion is the point at which something enters the pipeline, which is what keeps pipeline totals meaningful.
Archiving
Leads that go nowhere are archived rather than deleted, so the record of having tried survives. Archived leads are excluded from the active list.
Visibility
Leads follow the same visibility model as other records. See Visibility groups.