The North American Industry Classification System or NAICS is used by business and government to classify business establishments according to type of economic activity or type of industy
The codes are 6 digits long, but you can use just part of the code in order to search a broader group of industries. For instance, "Confectionery Manufacturing from Purchased Chocolate" has the code 311330, but the shorter 3113 works for all of the different industries that fall under "Sugar and Confectionery Product Manufacturing". If you're searching using an NAICS code and you're not finding much, try lopping a digit or two off of the end of the full 6-digit code and you may have better luck.
Just like at McDonald's, sometimes it's easier to order by number instead of by name. You can search in Business Source Complete by searching for your NAICS code and choosing "IC NAICS Code or Description" from the drop-down menus on the main search screen. Likewise, Hoover's includes NAICS codes in its search interface.
The next-easiest thing is to go into the printed reference book that lists all the NAICS codes, shelved at REF HF1041.5 .N67 2012. The table of contents and index are very useful.
Nested lists of NAICS codes can be found on the NAICS section of the Census website, but the keyword search tool does not work very well or intuitively - it's usually easier to start with the printed book, if you weren't able to find the NAICS for a similar company on Hoover's.
|11||Agriculture, Forestry, Fishing and Hunting|
|21||Mining, Quarrying, and Oil and Gas Extraction|
|48-49||Transportation and Warehousing|
|52||Finance and Insurance|
|53||Real Estate and Rental and Leasing|
|54||Professional, Scientific, and Technical Services|
|55||Management of Companies and Enterprises|
|56||Administrative and Support and Waste Management and Remediation Services|
|62||Health Care and Social Assistance|
|71||Arts, Entertainment, and Recreation|
|72||Accommodation and Food Services|
|81||Other Services (except Public Administration)|