What is Bubble Act?

Legal Definition
Bubble Act 1720 (also Royal Exchange and London Assurance Corporation Act 1719) (6 Geo I, c 18) was an Act of the Parliament of Great Britain passed on 11 June 1720 that incorporated the Royal Exchange and London Assurance Corporation, but more significantly forbade the formation of any other joint-stock companies unless approved by royal charter. Its provisions were extended later by the Bubble Schemes, Colonies Act 1740 (14 Geo. II, c. 37) to include its colonies, particularly Massachusetts.
-- Wikipedia
Legal Definition
Eng. law. The name given to the statute 6 Geo. I., c. 18, which was passed in 1719, and was intended " for restraining several extravagant and unwarrantable practices therein mentioned." See 2 P. Wms. 219.
-- Bouviers Law Dictionary
Legal Definition
The statute 6 Geo. I. c. 18, "fur restraining several extravagant and unwarrantable practices herein mentioned," was so called. It prescribed penalties for the formation of companies with little or no capital, with, the intention, by means of alluring advertisements, of obtaining money from the public by the sale of shares. Such undertakings were then commonly called "bubbles." This legislation was prompted by the collapse of the "South Sea Project," which, as Blackstone says, "had oeggared half the nation." It was mostly repealed by the statute 6 Geo. IV. c. 91.
-- Black's Law Dictionary