A package installer is a software tool that helps you install programs or applications on your computer. It takes care of all the necessary steps and settings so you can easily add new software onto your system. Full definition
This message will say «App installed from the Google Play Store» if you grabbed it through official channels, or «App installed from package installer» if the app was sideloaded. (android.gadgethacks.com)
Just ensure to hit the «package installer» when getting the prompt to install. (mytabletsupport.com)
This sounds basic but is actually a big improvement over Sony's older ereaders where you had to plug them into a computer and use Sony's desktop software or a package installer to install updates. (the-ebook-reader.com)