Business vertical

You can simply say a Business vertical is a business segment of a company, now the defination will make more sens

Further as per AS 17, Segment Reporting "A business segment is a part of the company that can be identified by the products it provides or by the services or geographical locations it operates in. In other words, it a single part of a business that can be distinctly separated from the company as a whole based on its customers, products, or market places. Management often divide companies into business segments to help determine which areas of the company are performing well and which areas need improvement."