Explanation
When a lead is converted in Salesforce, three new records are typically created: a contact, an account, and an opportunity. A contact is a person who is associated with an account and has a role in a sales process. An account is a company or organization that is a potential or existing customer. An opportunity is a sales deal that is in progress or has been closed. These records are linked together and use the information from the lead record. The lead record becomes read-only and is marked as converted. References:
Converting Leads
Lead Conversion in Salesforce