It´s just the histogram of the MACD. (Actually it´s not a histogram, I like the Area visualisation more. But you can switch.)
When I´m using the MACD, I´m just searching for a divergence between Price and the MACD-histogram. I´m not interested in the MACD-signalline or the MACD-line in any way. As you can see, The omission of them leads to better visualisation. It´s much easier to spot a divergence. On the one hand because that way the histogram scales bigger, on the other hand becauce the lines can´t overdraw the histogram.
Rules bullish Divergence: Price makes a lower low, oscillator makes higher low.
Rules bearish Divergence: Price makes a higher high, oscillator makes lower high.