Final answer:
A trial balloon is the process used in politics to gauge public reaction to an idea by informally introducing it, while a leak is the release of confidential information, often to influence opinion or policy.
Step-by-step explanation:
A trial balloon is a metaphor used in politics and media to describe the process of floating an idea or policy to the public, indirectly through the media or other channels, to observe the reaction. If the idea is met with approval, the individual or group behind the trial balloon might move forward with it; if not, they can back away without having formally committed to the concept.
On the other hand, a leak refers to the intentional or unintentional release of confidential information to the public or press. In the context of politics, it often indicates whistleblowing or a strategic move to influence public opinion or policy. Unlike a trial balloon, a leak might reveal information that the originator did not intend to disclose or might be part of a tactic to derail or promote a specific agenda.