Leads are obtained through referring a customer to another product or service or through direct response from publicity, including from advertising. Marketing is dependent upon leads for the growth of customers.
Every time a person accesses a website or links to advertisements within it, that could be considered a lead because the person has shown an interest in a specific product or service. Leads are at times shared with other businesses in order to increase the number of leads each business has. When a user buys something online or sets up an account with an e-commerce site they may be asked if they mind sharing their contact details with third parties. If they do not mind then their details will be shared and more advertising will follow.