根据我在Wikipedia上的查证，SSNIP是Small but Significant and Non-transitory Increase in Price的缩写，专业译法为“假定垄断者测试”，也可以直接写作SSNIP测试。

按照假定垄断者测试的方法，一个被假定的垄断者，在持续一段时间适度提高价格，结果消费者转向了其他替代品，那么替代品与诉争产品则属于同一市场，有竞争关系；反之，则不属于。

具体来讲，该测试首先假设在某个市场上存在这样一家企业，该企业是该商品或该类商品的唯一供应者。当该企业对其商品进行一个“小幅，但有意义的，且非临时性的涨价”时，如果客户选择了其他商品，从而使其涨价变得无利可图，因而阻止了该假定垄断者的这种涨价行为，那么相关产品市场就不能由这种商品单独构成，而应该将消费者最可能选择的替代品纳入待选市场，并且重新进行上述测试，直到最终达到一个临界点，使得这个供应有关产品或者服务的假定垄断者在这个点上获得市场支配力，即该假定垄断者可以通过将价格保持在平均水平之上而达到其利润的最大化。这个临界点通常就是划分相关产品市场的标准。有关这个测试中提到的涨价标准，一般而言采用5—10%作为常用幅度。

Wikipedia对SNNIP的解释如下：In competition law, before deciding whether companies have significant market power which would justify government intervention, the test of small but significant and non-transitory increase in price (SSNIP) is used to define the relevant market in a consistent way. It is an alternative to ad hoc determination of the relevant market by arguments about product similarity.

The SSNIP test is crucial in competition law cases accusing abuse of dominance and in approving or blocking mergers. Competition regulating authorities and other actuators of antitrust law intend to prevent market failure caused by cartel, oligopoly, monopoly, or other forms of market dominance.

我这里还查到了一个如何应用SNNIP测试的方法：

Applying SSNIP Test:

1 Start with smallest possible market and ask if 5% price increase profitable

2 If not, then firm does not have sufficient market power to raise price.

3 Next closest substitute is added to the relevant market and test repeated.

4 Process continues until the point is reached where a hypothetical monopolist could profitably impose a 5% price increase.

5 Market then defined.