android:hint="text"
provides an info for user that what he need to fill in particular editText
for example :- i have two edittext one for numeric value and other for string value . we can set a hint for user so he can understand that what value he needs to give
android:hint="Please enter phone number"
android:hint="Enter name"
after running app these two edittext will show the entered hint ,after click on edit text it goes and user can enter what he want (see luxurymode image)