Any contact or information that has potential to generate revenue/income for any business is a lead for that business. Example: if you are an AC mechanic, any person whose AC is not behaving well is your lead.
Not every lead is a serious customer. Some want to check prices and know more about it from you and patronize others while some might do that with others but patronize you. Nevertheless, give your best deal and talk nicely to every potential customer, if not this, another lead will definitely fall in love with your service and patronize.