Just like what title you wrote in this topic, it is a burning address where no one own that address and no one have access to it. It used as a method to reduce the number of tokens which they believe can help the price of token it self.
It is not just reducing the number of tokens, but if we think more about burning, we can say it is a buyback too.
When you want to burn the coin, you must buy in the market and collect them to burn.
This makes the coin price increase, because the buyback and burn.