Activity is the building block of the user interface. You
can think of an activity as being the Android analogue for the window
or dialog box in a desktop application or the page in a classic web
application. Android is designed to support lots of cheap activities, so
you can allow users to keep tapping to open new activities and
tapping the Back button to back up, just like they do in a web browser.
Please find more Topics on Android here www.androidtutorial.in