The Monthly DL finally provides you with a more concrete estimation of the real download potential behind a keyword.
The number on the right indicates the total number of monthly organic downloads driven by a given keyword across all app results.
The number on the left shows how many of those organic downloads your app is actually getting per month given its rank on that keyword. The higher the rank, the higher the share your app will get.
You can also check our ASO blog for tips on deeper keyword research and analysis