Manage business contacts that aren't (yet) clients — leads, prospects, suppliers' AP people, accountants, technicians. Separate from Clients (who can buy) and Suppliers (who you buy from).
Contacts → New Contact. Name, role, organisation, phone, email, notes.
Tag contacts (Lead, Prospect, Vendor-AP, Internal, etc.) so you can filter the list and target communications.
A contact can belong to a Client/Supplier company — useful for B2B where you have multiple contacts at one account.
Log calls/meetings/emails per contact. Feeds the CRM activity timeline if the contact is later promoted to a deal.