Activities are basically the applications that fill the screen for user interaction, it can be the Launcher, Phone Dialer or the Facebook application. At any given instance, the Activity window show one screen at a time and if you switch between them, the previous Activity window stored in the RAM memory will be loaded or a new Activity window is loaded, this is a helpful feature because initially when loading any application all of its resources are loaded in to the RAM, like code, scripts, services, media. As can be seen, this is an Intensive Task and consumes CPU cycles and RAM memory. When an application is closed, like when you switch from
