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, where you see a business opportunity with the lead, (i.e. when there is a chance of further negotiations with the lead), it can be converted into account, contact, and potential.
You can view the list of converted leads by selecting the Converted Leads List View.
Once the lead is converted to account, contact and potential, you cannot revert it.