A pure-play company has a single business focus. Ballard Power Systems (NASDAQ:BLDP) is a pure play in the fuel-cell industry, while firms that have fingers in the fuel-cell pie, along with other pies, include General Electric (NYSE:GE) and United Technologies (NYSE:UTX).

Until it was snapped up by Unilever (NYSE:UL) a few years ago, Ben & Jerry's was an ice cream pure play. Compare that to conglomerate ConAgra (NYSE:CAG), owner of the Healthy Choice brand, which includes ice cream, as well as other disparate businesses such as Butterball turkeys, Hebrew National hot dogs, Hunt's tomato products, Jiffy Pop popcorn, and LaChoy Chinese foods. In networking equipment, Cisco Systems (NASDAQ:CSCO) is a pure play, whereas Nokia (NYSE:NOK) is involved in networking equipment and other operations.

When investors are drawn to a particular kind of business, they may seek out a company that's a pure play so their invested dollars won't be spread out over other less desirable business segments. Of course, it can also make sense for investors to favor some conglomerates because of their diversification. If one business line falters, others will bolster the company.