A random number is one drawn from a set of restricted or infinite numbers with no evident pattern for prediction. The pool of numbers is virtually always independent of one another. However, the pool of numbers may have a specific distribution. For example, the heights of pupils in a school typically follow a normal distribution around the median height. If a student's height is chosen at random, the selected number is more likely to be closer to the median height than to be labelled as very tall or very short. The random number generators listed above assume that the numbers generated are independent of one another and will be evenly distributed across the entire range of values.
A random number generator, such as the ones shown above, is a device that can produce one or more random numbers within a specific range. Random number generators may be hardware-based or pseudo-random number generators. Hardware-based random-number generators can use a dice, a coin to flip, or a variety of different devices.
A pseudo-random number generator is an algorithm that generates a sequence of numbers with qualities similar to those of random numbers. Almost all computer-based random number generators generate pseudo-random numbers. However, the numbers produced by pseudo-random number generators are not actually random. Similarly, the generators listed above generate pseudo-random numbers. The random numbers generated are adequate for most applications; however, they should not be used for cryptographic reasons. True random numbers are based on physical events such as air noise, thermal noise, and other quantum effects. Methods for generating real random numbers include correcting for any measurement biases.