ASO is app store optimization which is the process of improving the visibility of a mobile app in app stores like iTunes and Google Play. There are two types of ASO - on-page optimization which involves optimizing the app name, description, category, keywords and metadata, and off-page optimization which focuses on improving the app's popularity, downloads and including screenshots. Tools like keyword rankings, keyword spy, install reports and analytics help track an app's performance and see how competitors are optimizing.