What is a "half" in Bitcoin? I saw in an article something about a Bitcoin algorithm half in 2020. What exactly is this? I have tried looking this up but I couldn't find anything that told me what it was only a website counting down to the next.
Bitcoin controls the supply of coins by halving the miner subsidy (reward) every 210,000 blocks or roughly every 4 years. The miner subsidy started at 50BTC. See Mining Reward.

This is a simple chart that illustrates the Bitcoin distribution schedule: