A trial balloon is information sent out to the media in order to observe the reaction of an audience. It can be used by companies sending out press releases to judge reaction by customers, or it can be used by politicians who deliberately leak information on a policy change under consideration. In politics trial balloons often take the form of an intentional news "leak" to assess public opinion.
For instance, a company might announce they are going to release a new computer program in a year, and then read the press coverage for hints on whether or not the product will have appeal in the marketplace. If the coverage is favourable the money will be spent on development, but if not the project can be cancelled before using up resources. A trial balloon under the company's own name is somewhat risky; if too many are "floated" the company risks becoming known as the company that cried wolf, and can find itself being ignored completely. In addition, the company can find that the product being planned is unworkable, leading to the phenomenon of vaporware.