What is "Keyword Library"?

Keyword Volume:
Indicates the number of times this term is searched for (on a scale of 100) by people using mobile devices with full internet browsers in each country.
Hits:
The number of actual search results (apps) returned when you search for a term. The graph depicts the number of search results returned on a scale of 100. If you do not see the "Hits" score, it's because we don't have the data....yet.
Keyword Efficiency Index (KEI):
This score indicates this keyword’s potential to drive traffic to your app. A keyword with high volume and low competition (Hits) would result in a higher efficiency score. For Japan, we use a keyword’s number of appearances across all apps as a proxy for volume.