What is the keyword volume? That's the number of search requests related to the keyword monthly. There is a close connection between the length of the keyword and the volume of unique searchers by them. The shorter the keyword is, the more times it will be used in search. it will be shown in impressions.
At first glance, it seems that high search volume is exactly what you need to aim/target in your promotion. Yes, it is right. Let's solve the case: we need to decide what is better: 1 keyword "money" with, let us say, 2 mil searchers monthly and "earn money app" "make money online", "make money app free" with 50,000 monthly searches each.
2 mln to 0,05 mln in a rather impressive number of visitors. But how many of them will be ready to download exactly your app after the related search request? 150,000 searches give more conversions – downloads and fine in-app activity that the audience you get from the all 2,000,000. It happens so that naturally less people are ready to download a certain app. But the more specific and to the matter the keyword is, the higher is the possibility that users will download the app, rate and review it, buy something or click the ads you place there.