Random Number

For the purposes of this recommendation, a value in a set that has an equal probability of being selected from the total population of possibilities and, hence, is unpredictable. A random number is an instance of an unbiased random variable, that is, the output produced by a uniformly distributed random process. 

See NIST SP 800-90A Rev. 1 for detailed information. 
 
A value in a set of numbers that has an equal probability of being selected from the total population of possibilities and, in that sense, is unpredictable. A random number is an instance of an unbiased random variable, that is, the output produced by a uniformly distributed random process. Random numbers may, e.g., be obtained by converting suitable strings of random bits. 

See NIST SP 800-107 Rev. 1 under Random number for detailed information.