A lead is a company or contact with the journey status Lead. Upsales applies this status automatically to every new company and contact.
An MQL (Marketing Qualified Lead) is a lead that matches the criteria you set up in your Journey configuration. Contacts that match the criteria get the MQL status automatically, so you can qualify leads based on their data and behavior before assigning them to a user.
The MQL status requires the Marketing Automation add-on. Without it, the next status after Lead is Assigned, which is applied when a user is assigned to the company.