Associations
The links between CRM records, such as a contact and the company they work for, or a deal and the people involved in it.
In HubSpot, contacts, companies and deals are separate objects. Associations connect them: a contact is associated with its company, a deal with its contacts and company.
Missing associations are a common data quality issue. A deal with no contact can't be followed up, a company with no contact can't be reached, and reports by company miss the deals that aren't attached to one.
Associations are also a source of data: an empty field on a contact, such as the company name, can often be filled from the company it's associated with.