According to the Merriam-Webster online dictionary, a bubble is a small globule typically hollow and light, a small body of gas within a liquid; a thin film of liquid inflated with air or gas; a globule in a transparent solid; something (as a plastic or inflatable structure) that is hemispherical or semi-cylindrical.
Then there are the darker definitions: something that lacks firmness, solidity, or reality; a delusive scheme; a state of booming economic activity (as in a stock market) that often ends in a sudden collapse.
Tiny bubbles made the late singer Don Ho happy. Lawrence Welk liked tiny bubbles, too. Financial Markets always want more of everything, however, so they prefer big bubbles: the kind that eventually explode into financial disaster for the many, but shower the very few who inflated and carefully manipulated those bubbles with enormous wealth.
In the early 20th Century, mass manufacturing of innovative products to make them cheaper to buy with easy credit, along with stocks purchases through margin loans offered by brokers, created the first of the century's burst bubbles, resulting in the Great Depression. Then came the Japanese bubble of the 1980s, expanded by deregulated financial markets, relaxed monetary policy, easy credit and low interest rates on an increased money supply that allowed massive financial market speculation in land and corporate profit values until, in May 1989, worried about the unsustainable values of land and stocks, the Japanese government decided to tighten monetary policy through a series of hikes in interest rates. The markets cooled, the bubble burst, recession followed, and the Japanese economy has yet to completely recover.