Irrational exuberance is people 's behaviour that are based on the psychology which diverges from rational perspective and this phenomenon move the market in one direction without any solid underlying facts.
Irrational exuberance is not the kind of investor euphoria or madness described by some story tellers who chronicled earlier. speculative excesses like the stock boom of 1920s . Perhaps those story tellers embellishing the story. Irrational exuberance is not that crazy. The one popular terms speculative mania or speculative orgy seemed too strong to describe what we were going through in 1990s. Irrational exuberance is quite descriptive term for what happens in markets when they get out of line.
By- Robert Schiller (book - irrational exuberance)