In mid 2016, the block reward will undergo its second halving, from 25 BTC per block, to 12.5.
This means that miners get half as much bitcoin as before. The bitcoin inflation rate will be half as much as before.
When this occurs, some combination of these two things MUST occur:
* Some miners who are now unprofitable turn off their miners, reducing difficulty and helping other miners survive.
* Bitcoin price increases (due to lower inflation, etc), making miners more profitable again.
We already had one halving, in late 2012. It helped to catalyze the 2013 bull market. (It was just one factor, of course. It would be silly to say it was the whole reason for the rise).