<category android:name="android.intent.category.HOME"/>
indicates that when you press home button, your app will be listed as an option to launch the launcher home or your home activity (along with all the applications which have this category in their manifest for an activity). To be more simple, whenever you press the home button, all the applications installed in your phone which have CATEGORY.HOME category and Action_Main in intent-filter in their AndroidManifest.xml will be listed (unless you have chosen some application as default) in a chooser for the user to select which HOME they want to launch.
