Many apps tend to accumulate over a period of time, but Google recognizes them and continues to show them in the section "Other apps" in the Play Store. That makes complete sense for paid apps which you have bought, but it might be unnecessary for a lot of free apps.
To clean this list, open Google Play on your mobile, and on the top right, tap on the Settings option and select ‘My apps’. In the view, select ‘All’. Apps that are not installed any more can then be removed. You can select an app that is still installed by touching the icon and selecting the ‘Uninstall’ option on the following page. The app will then be marked in the list to the right with a crossed circle. Several apps can be marked simultaneously by tapping and holding any one initially. Then simply tap on the delete symbol on the top right and confirm the question for removal.