AccountContactRelationship

This object is used to associate a single a single contact record to multiple account records so you can easily track the relationships between the people and businesses they work with.

The AccountContactRelation object supports person accounts. That means that a person account can be either a related contact on a business account or a related account on a contact. A person account can also be related to another person account as either a related contact or related account.

You can query AccountContactRelation records in your developer org, below query will give you the accountcontactrelation record info.

SELECT Id, ContactId, Contact.Name, AccountId, Account.Name FROM AccountContactRelation

You will have to enable setting Allow users to relate a contact to multiple accounts” setting from setup > account settings for above query to work.

You cannot delete AccountContactRelation record, only way to delete the records is to remove the account reference from contact.

Reference: Salesforce