What is the difference between dp and dip?

I am currently using following image view - ``` <ImageView android:id="@+id/flag" android:layout_width="120dp" android:layout_height="120dp" android:background="#000000" /> ``` but i am a little confused about what to use `dp` or `dip`? so that it changes from device to device say it should manage screen dimensions like for `320 x 640` Or is there anything else to manage it thanks in advance