A stalking horse is a figure used to test a concept or mount a challenge on behalf of a third party. If the idea proves viable or popular, the third party can then declare its interest and advance the concept with little risk of failure. If the concept fails, the third party will not be tainted by association with the failed concept and can either drop the idea completely or bide its time and wait until a better moment for launching an attack. The relationship between the stalking horse and third party is usually, but not always, hidden from the public. In many cases, the scheme is one-sided, with only one party aware of the arrangement.
In hunting, it refers to a horse, or a model of a horse, behind which a hunter hides when stalking game.