Android Terminology

Activity--UI in your app

View -- Interactive UI Components --Buttons,Labels,textfields

1)Widget--
View is the base class for widgets, which are used to create interactive UI components 

ex: Buttons,Checkboxes(Multi select),RadioButtons(Single select),ProgressBars,Spinners (Drop Down)
,EditText(Textbox-input),Textview(Labels-output),

2) Layout-- where to set the widgets --like the button,label etc is left or center etc
ViewGroup subclass is the base class for layouts, which are invisible containers that hold other Views 

Event --Action that occurs when user interacts with widgets
             ex: Button click etc