What is the meaning of android.intent.action.MAIN?

Question

I have seen so many different confusing explenations..

Answer 1

Is the main activity for this application

It is in the LAUNCHER category, meaning it gets an icon in anything that thinks of itself as a “launcher”, such as the home screen

The call to startActivity() will always add the DEFAULT category if no other category is specified.

Generally just add android.intent.category.DEFAULT even if you have other Categories. This will guarantee that if Requesting Intent doesn't provide any Categories while starting the intent using startActivity(intent), then your Receiving Activity can also receive those Intents..

Source: The Busy Coders Guide to Android Development

https://commonsware.com/Android/