Owners

HubSpot uses owners to assign specific users to contacts, companies, deals, tickets, or engagements. Any HubSpot user with access to contacts can be assigned as an owner, and multiple owners can be assigned to an object by creating a custom property for this purpose. Owners can only be created in HubSpot, but you can use the owners endpoints to get their identifying details, including IDs and email addresses. This data can then be assigned to CRM records in HubSpot or via property change API calls. 

Example use case: When you use these endpoints to get the IDs of owners in HubSpot, your integration can assign them to records.

Salesforce integration users

HubSpot owners and HubSpot users (people who can log into HubSpot) aren’t necessarily the same, as you may have owners created through the Salesforce integration.