1. A thin hollow bead or globe filled with air or gas: The soap bubbles were floating on top of the water and sometimes they would float in the air.

When a bottle of a soft drink is shaken, a lot of air bubbles can be seen going up to the top of the bottle.

2. A gurgling sound made by a boiling or effervescent liquid: While drinking Paul could hear a sound produced by bubbles forming and bursting.
3. A dome, usually made of transparent glass or plastic: The plastic bubble covered the cheese tray so the cheese wouldn't get dry.
4. The circle around the words said by people in a cartoon: The bubbles seen in cartoons contain the words that are spoken by the characters in the cartoon image or the cartoon strip.
5. A false feeling of confidence or security: Henry predicted that the rocketing housing market would be a bubble that would surely burst.
6. A risky or an unreliable business enterprise or speculative plan; especially, one that is fraudulent or unsuccessful: A lot of people suffered economically when the dot-com bubble burst.

There have been several times when people have invested money in something which has caused its value to rise to a level which is much higher than its real value until that bubble suddenly drops or bursts.

Is the rush for shares in the social-networking site for business professionals an uncomfortable echo of bubbles past? When an investor believes that other people would pay even more than the current high price for a stock, that's how bubbles develop.

1. To form or to produce round balls of air or gas; usually, inside a liquid: Water was bubbling or boiling in the kettle.
2. To flow with the quiet sounds of water moving over rocks: The brook was bubbling over the rocks and creating a wonderful sound.
3. To be very excited and happy: During the party, on the last day of school, the children were bubbling with excitement.
4. When emotions or feelings exist in a person without being shown to others: The winner of the prize seemed calm; however, his mother could see that her son was bubbling over with excitement about getting the trophy.