The amount of money that you win or receive from someone rather unexpectedly is called ‘windfall'. It's a sudden stroke of luck.
Fruit that falls down from a tree because of heavy wind is also called windfall.
In the old days in England, landowners were not allowed to cut down trees which were on their property. The law stipulated that all trees were the property of the Royal Navy, and the wood was to be used in constructing ships. If, however, heavy wind made a tree fall, the ‘windfall' became the owner's property. Since in the old days such ‘windfall' was not common, the word began to mean unexpected good fortune.
When Rita visited her uncle after her marriage, she got a windfall of Rs. 75000.
Sumit's garden was covered with windfalls.