Keyword promotion - is a process of installing your app by the required keyword (by which a user finds your app).
The keywords - are words or phrases that represent search queries for which the app is searched by users.
Also, keywords - are an integral part of app's optimization (ASO). The more keywords you write in the description - the more likely that users will find and install it. This is why keywords are very important.
The most important reason to use keyword installs traffic is due to its affect to the rank. It means that while users install your application via keywords, your apps' rank grows. Further it helps target users to find your application faster as it will be in the TOP of the rank. As a conclusion you can boost your app's rank faster and get a lot of organic installs soon after your application will appear on the Google Play Market.