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\,}
是隨機變數 
小於或等於指定值 
的機率。
將代表隨機值 在從具有 的分佈中選擇隨機值時出現的分佈或相對次數。