Short answer
Custom objects are database tables you add to a CRM to store business data that standard objects such as contacts, companies and deals don't cover, for example properties, policies, funds or financial accounts. Salesforce supports them broadly; HubSpot requires an Enterprise edition.
Custom Objects explained
A custom object has its own fields, page layouts, permissions and relationships to other records, and appears in reports and automation like any standard object. Creating one is the right choice when the data has its own lifecycle and many records relate to one contact or company. When you only need a few extra details, custom fields or properties are simpler.
Each platform has limits on the number of custom objects, so design matters in large orgs.
How Vantage Point helps: we design custom object models in Salesforce and HubSpot and migrate data into them.
Frequently asked questions
Which HubSpot edition supports custom objects?
Custom objects are available on HubSpot Enterprise editions.
When should I use a custom object instead of a custom field?
Use a custom object when the data has its own records and lifecycle, such as many policies per client. Use a field for a single attribute.