在概率论和统计学中，几何分布（Geometric distribution）指的是以下两种离散型zh-hans:概率分布中的一种：

实际使用中指的是哪一个取决于惯例和使用方便。

这两种分布不应该混淆。前一种形式（X的分布）经常被称作shifted geometric distribution；但是，为了避免歧义，最好明确地说明取值范围。

如果每次试验的成功概率是p，那幺k次试验中，第k次才得到成功的概率是，

其中k = 1, 2, 3, ....

上式描述的是取得一次成功所需要的试验次数。而另一种形式，也就是第一次成功之前所失败的次数，可以写为，

In probability theory and statistics, the geometric distribution is either of two discrete probability distributions:

Which of these one calls "the" geometric distribution is a matter of convention and convenience.

These two different geometric distributions should not be confused with each other. Often, the name shifted geometric distribution is adopted for the former one (distribution of the number X); however, to avoid ambiguity, it is considered wise to indicate which is intended, by mentioning the support explicitly.