A lead is a prospective customer interested in purchasing your organization’s products or services. During the follow-up process, when you reach a certain stage, like a business opportunity with the lead, (i.e. when there is a chance of further negotiations with the lead), it can be converted to an account, contact, and deal.
You can view the list of converted leads by selecting the Converted Leads List View.
Once the lead is converted to an account, contact and deal, you cannot revert it.