Long shot is an attempt or guess that has only the slightest chance of succeeding or being accurate.
"it's a long shot, but well worth trying"
On a long or establishing shot, your face isn’t very visible - so your whole body comes your greatest form of expression. In a long shot, subtlety is out the window. So don’t bother with it. You can be much bigger than you would normally be.
In film, a view of a scene that is shot from a considerable distance, so that people appear as indistinct shapes. An extreme long shot is a view from an even greater distance, in which people appear as small dots in the landscape if at all (eg. a shot of New York's skyline).