While a marketing strategy is related to a marketing plan, they are two different things.
A marketing plan is a more detailed document that outlines the specific types of marketing activities you will use and timetables for different events and campaigns. Marketing strategy covers the big picture, where as your marketing plan will outline the specifics of how you plan to reach specific business goals.
Your marketing strategy should last longer than your business plan. A business plan is designed to change or be replaced over time, whereas a marketing strategy is more long-lasting.