What is the difference between a business case and a business plan?

Simply, a business case is a supported argument that a business-related concept is both practical and profitable (in any sense), while a business plan contains and demonstrates the financial steps necessary to create or grow a successful business or successfully carry out a business activity. For example, you could make a business case for investing in billboard advertising for your motel. You would cite the success other motels have had from such advertising. You could make a business case for opening a Frozen Yogurt shop in downtown Phoenix, but it might be harder to make a good business case for opening your shop in Anchorage. A business plan will do two things. First, it will be your guide to creating or growing your business. It will address every major aspect, especially those related to expenses and income over time. Second, it will demonstrate to you and to others (such as potential partners and investors) the value--profitability--of your idea and your approach. The above is a layman's introduction to these topics, about which much more can be said.