F X ( x ) : X is a random variable having c d f = P ( X ≤ x ) for some value x {\displaystyle F_{X}(x):X{\mbox{ is a random variable having }}cdf=P(X\leq x){\mbox{ for some value }}x\,}
f X ( x ) : X is a random variable having p d f value for a specific random value x {\displaystyle f_{X}(x):X{\mbox{ is a random variable having }}pdf{\mbox{ value for a specific random value }}x\,}
是随机变量 
小于或等于指定值 
的概率。
将代表随机值 在从具有 的分布中选择随机值时出现的分布或相对次数。