Marketing is actively promoting the brand, product and or service in a direct or indirect manner usually with the goal of identifying potential clients or advancing a corporate message (brand, investor sentiment, etc).
Business development identifies strategic partnerships and opportunities within and across segments or industries. Some of these opportunities are transferred to Marketing or Sales for closing.
Sales turns prospects into customers and keeps existing customers with the company. They are the customer advocate within the company and are a strong feedback source for Marketing and BizDev.
Closing is securing a deal. For Sales, that’s usually a transaction in the form of monetary exchange or signing a contract. For BizDev, it’s usually a partnership agreement.