What is the difference between main activity and regular activity in Android?

In Android, the term "main activity" usually refers to the activity that is launched first when starting the app — it is declared in the manifest with an intent filter for the MAIN action and LAUNCHER category.

A regular activity is any other activity in the app that is launched from the main or other activities.

Differences:

• Main activity — entry point of the app, shown in the device's app list.
• Regular activity — used to display various screens within the app, not launched directly from the launcher.

Example from AndroidManifest.xml:

<activity android:name=".MainActivity">
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
</activity>

<activity android:name=".SecondActivity" />

Here, MainActivity is the main activity, SecondActivity is a regular one.