Few years ago some economic specialist says Bitcoin is a huge bubble.
why they said it? and what is the meaning of the bubble?
you can know it was a bubble only after it has popped. In case of Bitcoin it may not be a bubble, it just attracts more and more people and if it is truely used throughout the world as a medium of exchange its price is sustainable.
But if it is a bubble, than one day you will hear a loud POP and the price of Bitcoin goes down to 100USD or even possibly 10cents