Difference between true & pseudo random numbers

I recently heard that in Linux, /dev/random and /dev/urandom are pseudo random number generators but not true random number generator.

So I am curious to know the difference between pseudo & true random number? In other words What is the difference between pseudo-randomness & true-randomness?

• This could largely be answered by a Google search. Do you have a more specific question about this related to computational science? – horchler Mar 25 '16 at 15:07
• @horchler If this question is more suitable on other (SE) site (example-Unix & Linux) then tell/suggest me – Pandya Mar 29 '16 at 5:09
• Wikipedia article Pseudorandom number generator – Steve May 26 '16 at 10:51