Sentence:  Tossing a coin is a classical procedure for producing a <WSD>random number</WSD> .... Tossing a coin 20 times can produce any one of 220 ... binary series, and each of them has exactly the same probability. 
Meaning of the word marked with <WSD> tags:  A number selected based on a uniform distribution, typically using a suitable generator (for example, rolling a die).