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But could you please explain what "halving" mean exactly please ? thanks
Right now, the block subsidy paid to miners is 25 BTC for each block solved. Since blocks are solved on average every 10 minutes, this means that 3,600 brand new bitcoins come into existence every day.
After block number 419999 (which is likely to occur somewhere around July of 2016), then block subsidy will be reduced to 12.5 BTC for each block solved. That means that only 1,800 brand new bitcoins will come into existence every day.
If there are less bitcoins available to be bought,
and if there is demand for the same amount (or an increased amount) of bitcoins, then the bitcoins that are available become more valuable. If ten people want an orange, and there are 100 oranges, then the seller might only be able to convince people to pay $0.10 for an orange. If those same ten people want an orange, and there are only 4 oranges, then four of the ten people might be willing to pay a bit more for the orange to convince the seller to sell to them instead of one of the other buyers. Bitcoins work the same way. If there aren't enough bitcoins available for everyone that wants them at the current price, then the price goes up until the number of bitcoins desired at that price matches the number of bitcoins available at that price. If there are more bitcoins available than people want at the current price, then the price goes down until the number of bitcoins available at the new price matches the number of bitcoins that people want at that price.
The block subsidy continues to be cut in half every 210,000 blocks. At an average of 10 minutes per block, this means that there are approximately 4 years between "halvings". So it will be reduced to 6.25 BTC per block after block 629999 (somewhere in the year 2020) and to 3.124 after block 839999 (somewhere in the year 2024).
Eventually, somewhere around the year 2136 after block 6719999 is solved the block subsidy will be reduced from 0.00000002 BTC to 0.00000001 BTC. Four years after that, somewhere around the year 2140 after block 6929999, the block subsidy will be reduced from 0.00000001 BTC to 0 BTC. After that, there will never be any more bitcoins (or fractions of bitcoins) coming into existence.