Business Support is often called BPO, of business process outsourcing, and it includes all the activities which does not form part of your core business. As such, these functions can be outsourced to third parties or contractors.
For example, if you are in the business of “manufacturing garden furniture”, everything you would need to do so, is regarded as business support. This includes, sourcing of machinery, plant and equipment, the maintenance of these machines, the sourcing of raw materials like steel, or wood, as well as the administration of your business.
Marketing and Sales are also support functions, but the marketing of your product or brand name must happen before you will even get an order for new furniture. Sales then follows, when your marketing efforts have created the need for your products.
Business Support however excludes Human Capital and Finance, as these are core functions needed to run a business. There are certain aspects that you can outsource, like auditing of your financial statements or the recruitment of new staff or temporary employment, but money and people remain your largest assets and must be managed properly.