Standard objects are objects that are included with Salesforce by default, such as Account, Contact, Lead, Opportunity, etc. They have predefined fields and functionality that support common business processes. Custom objects are objects that you create to store information that is specific to your organization or industry. You can create new standard objects using the Object Manager in Setup. Reference: https://trailhead.salesforce.com/en/content/learn/modules/data_modeling/standard_and_custom_objects