A concept is an idea. You think that your neighborhood could use a good widget store and an idea is conceived: Why don't you start a widget store? From then on, your concept can grow until the question is answered. The possible answers to the question are:
There is already a good widget store nearby.
You don't have enough money to start and run a good widget store.
There isn't enough profit in selling widgets to pay the costs of a store.
You'd rather sell wholesale widgets.
Actually, there are no good reasons not to.
Your business concept will eventually become part of your plan's executive summary. For now, it is the core of your business idea. It is a summary of your question rephrased: Is a widget store in this neighborhood a viable business opportunity for me? To accurately answer that question, another list of questions must be answered:
What is the local market for widgets?
Is that market being satisfied?
Are widgets profitable?
How can they be made more profitable?
Is this a business I am qualified to operate?
Do I have the capital to start and operate this business?
Do I want to start and run a widget store?
How will owning a widget store change my life?
These questions will lead to others, each requiring an answer before a decision can be made. Your business plan is a document written to convince yourself and possibly others that such a business concept is viable. If it isn't, the business plan won't get finished.
Here's an example of a business concept from Appendix B:
Acme Time Management Consultants, Inc. (ATMC), incorporated under the laws of the State of New York, is a start-up company seeking to establish itself in the professional organizing service industry.
You can download sample executive summaries from actual business plans at various websites on the Internet. AllBusiness.com offers many executive summaries for free, though there is a fee for downloading full sample business plans. In addition, many business schools have sample business plans and executive summaries available at no cost.