Typically, when doing research in marketing we are talking about conducting market research. According to Entrepreneur's Small Business Encyclopedia, market research is: 

The process of gathering, analyzing and interpreting information about a market, about a product or service to be offered for sale in that market, and about the past, present and potential customers for the product or service; research into the characteristics, spending habits, location and needs of your business's target market, the industry as a whole, and the particular competitors you face (source)

Conducting Market Research can help you answer questions like: 

• What is the size of my market?
• Who are my competitors?
• Which market is best suited for my product or service?
• How much will customers pay for my product or service?
• What are the emerging trends in an industry?

Marketing, however, is also an entire academic field with rich scholarship and insight. While many of the resources and strategies represented in this guide refer to Market Research, as defined above, suggestions for conducting research within the field of marketing are also provided. As always, don't hesitate to reach out to your library liaison with any questions.  

When using databases, journals, articles, etc. found in the library you are most likely engaging in secondary market research.

Secondary market research is made up of information, data, and more that has been collected by someone else and analyzed to various extents. This research can come from educational, institutional, or commercial sources so it is imperative that you understand how the information was collected and analyzed, who is sharing the information now, and why they are sharing this information. Secondary market research can often be broken down further into information about the company, information about the market (which, when used this way, means the world or environment in which business is done), and information about the customer or consumer.  When combined with your own knowledge and insight - whether from primary research and/or experience - secondary market research can help further inform and inspire your own original analysis into a specific problem or situation.  

Original market research - such as conducting interviews, surveys, focus groups, or observational studies yourself (or hiring someone to do so) is considered primary market research. While generally more specific and detailed then what may be uncovered through secondary market research, primary market research can be more time consuming and/or costly. 

The best kind of market research is a combination of primary and secondary market research.