You need to explain the type of business you're in. You'll be expected to explain the general state of your industry and the nature of the business, especially if your plan is going outside your company to banks or investors.
Everything in your industry that happens outside of your business will affect your company. The more you know about your industry the more advantage and protection you will have. A complete business plan discusses general industry economics, participants, distribution patterns, factors in the competition, and whatever else describes the nature of this business to outsiders.
The Internet has had an enormous impact on the state of business information. Finding information isn't really the problem any more, after the information explosion and the huge growth in the Internet beginning in the 1990s and continuing in the 21st Century. Even 10 or 15 years ago, dealing with information was more a problem of sorting through it all than of finding raw data. That generality is more true every day. There are Web sites for business analysis, financial statistics, demographics, trade associations, and just about everything you'll need for a complete business plan.
You should know who else sells in your market. You can't easily describe a type of business without describing the nature of the participants. There is a huge difference, for example, between an industry like broadband television services, in which there are only a few huge companies in any one country, and one like dry cleaning, in which there are tens of thousands of smaller participants.
This can make a big difference to a business and a business plan. The restaurant industry, for example, is what we call "pulverized," which, like the dry cleaning industry, is made up of many small participants. The fast food business, on the other hand, is composed of a few national brands participating in thousands of branded outlets, many of them franchised.