[Haskell-beginners] "pure" versus "impure" code

Hi Folks, Is there a web site that defines "pure" versus "impure" code? My understanding is that: - Pure code is code that does no I/O - Impure code is code that does I/O Is that correct? Also, it is my understanding that good software design is to isolate/separate the impure code from the pure code. Is that correct? Does that principle apply to all programming languages, or just Haskell? /Roger