Put simply the word 'bleh' is a verbal 'shrug'. It can be used for every situation that a shrug of one's shoulders can. Also it can be used to show signs of frustration, confusion, indecision and boredom. It is often used in reply to a question that you have no interest in answering or have no answer for, or in a situation where you don't know what to say so you simply 'shrug' it of by saying 'bleh'.
Question: What are your thoughts on the world's economical climate?