Lead generation, or lead gen is a marketing tool used, particularly in internet marketing, to generate consumer interest or inquiry into products or services of a business. wikipedia.org

Customer service is the provision of service to customers before, during and after a purchase. wikipedia.org

A sale is the act of selling a product or service in return for money or other compensation. It is an act of completion of a commercial activity. wikipedia.org

Cold calling is the marketing process of approaching prospective customers or clients, typically via telephone, who were not expecting such an interaction. wikipedia.org

A subset of the field of commerce, business development comprises a number of techniques and responsibilities which aim at: wikipedia.org

Telemarketing (sometimes known as inside sales, or telesales in the UK and Ireland) is a method of direct marketing in which a salesperson solicits prospective customers to buy products or services, either over the phone or through a subsequent face to face or Web conferencing appointment

Direct selling is the marketing and selling of products directly to consumers away from a fixed retail location.

Sales management is a business discipline which is focused on the practical application of sales techniques and the management of a firm's sales operations. wikipedia.org